Expressions can be used at several points in SQL statements, such as in the ORDER BY or HAVING clauses of SELECT statements, in the WHERE clause of a SELECT, DELETE, or UPDATE statement, or in SET statements. Expressions can be written using literal values, column values, NULL, built-in functions, user-defined functions, and operators. This chapter describes the functions and operators that are allowed for writing expressions in MySQL. Instructions for writing user-defined functions are given in Section 19.2, “Adding New Functions to MySQL”.

An expression that contains NULL always produces a NULL value unless otherwise indicated in the documentation for a particular function or operator.

Note: By default, there must be no whitespace between a function name and the parenthesis following it. This helps the MySQL parser distinguish between function calls and references to tables or columns that happen to have the same name as a function. However, spaces around function arguments are permitted.

You can tell the MySQL server to accept spaces after function names by starting it with the --sql-mode=IGNORE_SPACE option. (See Section 5.2.5, “The Server SQL Mode”.) Individual client programs can request this behavior by using the CLIENT_IGNORE_SPACE option for mysql_real_connect(). In either case, all function names become reserved words.

For the sake of brevity, most examples in this chapter display the output from the mysql program in abbreviated form. Rather than showing examples in this format:

mysql> SELECT MOD(29,9);
+-----------+
| mod(29,9) |
+-----------+
|         2 |
+-----------+
1 rows in set (0.00 sec)

This format is used instead:

mysql> SELECT MOD(29,9);
        -> 2

12.1. Operators

12.1.1. Operator Precedence
12.1.2. Type Conversion in Expression Evaluation
12.1.3. Comparison Functions and Operators
12.1.4. Logical Operators

12.1.1. Operator Precedence

Operator precedences are shown in the following list, from lowest precedence to the highest. Operators that are shown together on a line have the same precedence.

:=
||, OR, XOR
&&, AND
BETWEEN, CASE, WHEN, THEN, ELSE
=, <=>, >=, >, <=, <, <>, !=, IS, LIKE, REGEXP, IN
|
&
<<, >>
-, +
*, /, DIV, %, MOD
^
- (unary minus), ~ (unary bit inversion)
!, NOT
BINARY, COLLATE

The precedence of operators determines the order of evaluation of terms in an expression. To override this order and group terms explicitly, use parentheses. For example:

mysql> SELECT 1+2*3;
        -> 7
mysql> SELECT (1+2)*3;
        -> 9

12.1.2. Type Conversion in Expression Evaluation

When an operator is used with operands of different types, type conversion occurs to make the operands compatible. Some conversions occur implicitly. For example, MySQL automatically converts numbers to strings as necessary, and vice versa.

mysql> SELECT 1+'1';
        -> 2
mysql> SELECT CONCAT(2,' test');
        -> '2 test'

It is also possible to perform explicit conversions. If you want to convert a number to a string explicitly, use the CAST() or CONCAT() function (CAST() is preferable, but is unavailable before MySQL 4.0.2):

mysql> SELECT 38.8, CAST(38.8 AS CHAR);
        -> 38.8, '38.8'
mysql> SELECT 38.8, CONCAT(38.8);
        -> 38.8, '38.8'

The following rules describe how conversion occurs for comparison operations:

If one or both arguments are NULL, the result of the comparison is NULL, except for the NULL-safe <=> equality comparison operator. For NULL <=> NULL, the result is true.
If both arguments in a comparison operation are strings, they are compared as strings.
If both arguments are integers, they are compared as integers.
Hexadecimal values are treated as binary strings if not compared to a number.
If one of the arguments is a TIMESTAMP or DATETIME column and the other argument is a constant, the constant is converted to a timestamp before the comparison is performed. This is done to be more ODBC-friendly. Note that this is not done for the arguments to IN()! To be safe, always use complete datetime, date, or time strings when doing comparisons.
In all other cases, the arguments are compared as floating-point (real) numbers.

The following examples illustrate conversion of strings to numbers for comparison operations:

mysql> SELECT 1 > '6x';
        -> 0
mysql> SELECT 7 > '6x';
        -> 1
mysql> SELECT 0 > 'x6';
        -> 0
mysql> SELECT 0 = 'x6';
        -> 1

Note that when you are comparing a string column with a number, MySQL cannot use an index on the column to quickly look up the value. If str_col is an indexed string column, the index cannot be used when performing the lookup in the following statement:

SELECT * FROM tbl_name WHERE str_col=1;

The reason for this is that there are many different strings that may convert to the value 1, such as '1', ' 1', or '1a'.

Comparisons that use floating-point numbers (or values that are converted to floating-point numbers) are approximate because such numbers are inexact. This might lead to results that appear inconsistent:

mysql> SELECT '18015376320243458' = 18015376320243458;
        -> 1
mysql> SELECT '18015376320243459' = 18015376320243459;
        -> 0

Such results can occur because the values are converted to floating-point numbers, which have only 53 bits of precision and are subject to rounding:

mysql> SELECT '18015376320243459'+0.0;
        -> 1.8015376320243e+16

Furthermore, the conversion from string to floating-point and from integer to floating-point do not necessarily occur the same way. The integer may be converted to floating-point by the CPU, whereas the string is converted digit by digit in an operation that involves floating-point multiplications.

The results shown will vary on different systems, and can be affected by factors such as computer architecture or the compiler version or optimization level. One way to avoid such problems is to use CAST() so that a value will not be converted implicitly to a float-point number:

mysql> SELECT CAST('18015376320243459' AS UNSIGNED) = 18015376320243459;
        -> 1

For more information about floating-point comparisons, see Section A.5.8, “Problems with Floating-Point Comparisons”.

12.1.3. Comparison Functions and Operators

Comparison operations result in a value of 1 (TRUE), 0 (FALSE), or NULL. These operations work for both numbers and strings. Strings are automatically converted to numbers and numbers to strings as necessary.

Some of the functions in this section (such as LEAST() and GREATEST()) return values other than 1 (TRUE), 0 (FALSE), or NULL. However, the value they return is based on comparison operations performed according to the rules described in Section 12.1.2, “Type Conversion in Expression Evaluation”.

To convert a value to a specific type for comparison purposes, you can use the CAST() function. String values can be converted to a different character set using CONVERT(). See Section 12.8, “Cast Functions and Operators”.

By default, string comparisons are not case sensitive and use the current character set. The default is latin1 (cp1252 West European), which also works well for English.

=

Equal:

mysql> SELECT 1 = 0;
        -> 0
mysql> SELECT '0' = 0;
        -> 1
mysql> SELECT '0.0' = 0;
        -> 1
mysql> SELECT '0.01' = 0;
        -> 0
mysql> SELECT '.01' = 0.01;
        -> 1

<=>
NULL-safe equal. This operator performs an equality comparison like the = operator, but returns 1 rather than NULL if both operands are NULL, and 0 rather than NULL if one operand is NULL.
```
mysql> SELECT 1 <=> 1, NULL <=> NULL, 1 <=> NULL;
        -> 1, 1, 0
mysql> SELECT 1 = 1, NULL = NULL, 1 = NULL;
        -> 1, NULL, NULL
```
<=> was added in MySQL 3.23.0.

<>, !=

Not equal:

mysql> SELECT '.01' <> '0.01';
        -> 1
mysql> SELECT .01 <> '0.01';
        -> 0
mysql> SELECT 'zapp' <> 'zappp';
        -> 1

<=
Less than or equal:
```
mysql> SELECT 0.1 <= 2;
        -> 1
```
<
Less than:
```
mysql> SELECT 2 < 2;
        -> 0
```
>=
Greater than or equal:
```
mysql> SELECT 2 >= 2;
        -> 1
```
>
Greater than:
```
mysql> SELECT 2 > 2;
        -> 0
```
IS NULL, IS NOT NULL
Tests whether a value is or is not NULL.
```
mysql> SELECT 1 IS NULL, 0 IS NULL, NULL IS NULL;
        -> 0, 0, 1
mysql> SELECT 1 IS NOT NULL, 0 IS NOT NULL, NULL IS NOT NULL;
        -> 1, 1, 0
```
To work well with ODBC programs, MySQL supports the following extra features when using IS NULL:
- You can find the row that contains the most recent AUTO_INCREMENT value by issuing a statement of the following form immediately after generating the value:
```
SELECT * FROM tbl_name WHERE auto_col IS NULL
```
  This behavior can be disabled by setting SQL_AUTO_IS_NULL=0. See Section 13.5.3, “SET Syntax”.
- For DATE and DATETIME columns that are declared as NOT NULL, you can find the special date '0000-00-00' by using a statement like this:
```
SELECT * FROM tbl_name WHERE date_column IS NULL
```
  This is needed to get some ODBC applications to work because ODBC does not support a '0000-00-00' date value.
expr BETWEEN min AND max
If expr is greater than or equal to min and expr is less than or equal to max, BETWEEN returns 1, otherwise it returns 0. This is equivalent to the expression (min <= expr AND expr <= max) if all the arguments are of the same type. Otherwise type conversion takes place according to the rules described in Section 12.1.2, “Type Conversion in Expression Evaluation”, but applied to all the three arguments. Note: Before MySQL 4.0.5, arguments were converted to the type of expr instead.
```
mysql> SELECT 1 BETWEEN 2 AND 3;
        -> 0
mysql> SELECT 'b' BETWEEN 'a' AND 'c';
        -> 1
mysql> SELECT 2 BETWEEN 2 AND '3';
        -> 1
mysql> SELECT 2 BETWEEN 2 AND 'x-3';
        -> 0
```
expr NOT BETWEEN min AND max
This is the same as NOT (expr BETWEEN min AND max).
COALESCE(value,...)
Returns the first non-NULL value in the list, or NULL if there are no non-NULL values.
```
mysql> SELECT COALESCE(NULL,1);
        -> 1
mysql> SELECT COALESCE(NULL,NULL,NULL);
        -> NULL
```
COALESCE() was added in MySQL 3.23.3.
GREATEST(value1,value2,...)
With two or more arguments, returns the largest (maximum-valued) argument. The arguments are compared using the same rules as for LEAST().
```
mysql> SELECT GREATEST(2,0);
        -> 2
mysql> SELECT GREATEST(34.0,3.0,5.0,767.0);
        -> 767.0
mysql> SELECT GREATEST('B','A','C');
        -> 'C'
```
GREATEST() returns NULL only if all arguments are NULL.
Before MySQL 3.22.5, you can use MAX() instead of GREATEST().
expr IN (value,...)
Returns 1 if expr is equal to any of the values in the IN list, else returns 0. If all values are constants, they are evaluated according to the type of expr and sorted. The search for the item then is done using a binary search. This means IN is very quick if the IN value list consists entirely of constants. Otherwise, type conversion takes place according to the rules described in Section 12.1.2, “Type Conversion in Expression Evaluation”, but applied to all the arguments.
```
mysql> SELECT 2 IN (0,3,5,7);
        -> 0
mysql> SELECT 'wefwf' IN ('wee','wefwf','weg');
        -> 1
```
You should never mix quoted and unquoted values in an IN list because the comparison rules for quoted values (such as strings) and unquoted values (such as numbers) differ. Mixing types may therefore lead to inconsistent results. For example, do not write an IN expression like this:
```
SELECT val1 FROM tbl1 WHERE val1 IN (1,2,'a');
```
Instead, write it like this:
```
SELECT val1 FROM tbl1 WHERE val1 IN ('1','2','a');
```
The number of values in the IN list is only limited by the max_allowed_packet value.
To comply with the SQL standard, from MySQL 4.1.0 on IN returns NULL not only if the expression on the left hand side is NULL, but also if no match is found in the list and one of the expressions in the list is NULL.
From MySQL 4.1.0 on, IN() syntax can also be used to write certain types of subqueries. See Section 13.2.8.3, “Subqueries with ANY, IN, and SOME”.
expr NOT IN (value,...)
This is the same as NOT (expr IN (value,...)).
ISNULL(expr)
If expr is NULL, ISNULL() returns 1, otherwise it returns 0.
```
mysql> SELECT ISNULL(1+1);
        -> 0
mysql> SELECT ISNULL(1/0);
        -> 1
```
ISNULL() can be used instead of = to test whether a value is NULL. (Comparing a value to NULL using = always yields false.)
The ISNULL() function shares some special behaviors with the IS NULL comparison operator. See the description of IS NULL.
INTERVAL(N,N1,N2,N3,...)
Returns 0 if N < N1, 1 if N < N2 and so on or -1 if N is NULL. All arguments are treated as integers. It is required that N1 < N2 < N3 < ... < Nn for this function to work correctly. This is because a binary search is used (very fast).
```
mysql> SELECT INTERVAL(23, 1, 15, 17, 30, 44, 200);
        -> 3
mysql> SELECT INTERVAL(10, 1, 10, 100, 1000);
        -> 2
mysql> SELECT INTERVAL(22, 23, 30, 44, 200);
        -> 0
```
LEAST(value1,value2,...)
With two or more arguments, returns the smallest (minimum-valued) argument. The arguments are compared using the following rules:
- If the return value is used in an INTEGER context or all arguments are integer-valued, they are compared as integers.
- If the return value is used in a REAL context or all arguments are real-valued, they are compared as reals.
- If any argument is a case-sensitive string, the arguments are compared as case-sensitive strings.
- In all other cases, the arguments are compared as case-insensitive strings.
```
mysql> SELECT LEAST(2,0);
        -> 0
mysql> SELECT LEAST(34.0,3.0,5.0,767.0);
        -> 3.0
mysql> SELECT LEAST('B','A','C');
        -> 'A'
```
LEAST() returns NULL only if all arguments are NULL.
Before MySQL 3.22.5, you can use MIN() instead of LEAST().
Note that the preceding conversion rules can produce strange results in some borderline cases:
```
mysql> SELECT CAST(LEAST(3600, 9223372036854775808.0) as SIGNED);
        -> -9223372036854775808
```
This happens because MySQL reads 9223372036854775808.0 in an integer context. The integer representation is not good enough to hold the value, so it wraps to a signed integer.

12.1.4. Logical Operators

In SQL, all logical operators evaluate to TRUE, FALSE, or NULL (UNKNOWN). In MySQL, these are implemented as 1 (TRUE), 0 (FALSE), and NULL. Most of this is common to different SQL database servers, although some servers may return any non-zero value for TRUE.

NOT, !

Logical NOT. Evaluates to 1 if the operand is 0, to 0 if the operand is non-zero, and NOT NULL returns NULL.

mysql> SELECT NOT 10;
        -> 0
mysql> SELECT NOT 0;
        -> 1
mysql> SELECT NOT NULL;
        -> NULL
mysql> SELECT ! (1+1);
        -> 0
mysql> SELECT ! 1+1;
        -> 1

The last example produces 1 because the expression evaluates the same way as (!1)+1.

AND, &&
Logical AND. Evaluates to 1 if all operands are non-zero and not NULL, to 0 if one or more operands are 0, otherwise NULL is returned.
```
mysql> SELECT 1 && 1;
        -> 1
mysql> SELECT 1 && 0;
        -> 0
mysql> SELECT 1 && NULL;
        -> NULL
mysql> SELECT 0 && NULL;
        -> 0
mysql> SELECT NULL && 0;
        -> 0
```
Please note that MySQL versions prior to 4.0.5 stop evaluation when a NULL is encountered, rather than continuing the process to check for possible 0 values. This means that in these versions, SELECT (NULL AND 0) returns NULL instead of 0. As of MySQL 4.0.5, the code has been re-engineered so that the result is always as prescribed by the SQL standards while still using the optimization wherever possible.
OR, ||
Logical OR. When both operands are non-NULL, the result is 1 if any operand is non-zero, and 0 otherwise. With a NULL operand, the result is 1 if the other operand is non-zero, and NULL otherwise. If both operands are NULL, the result is NULL.
```
mysql> SELECT 1 || 1;
        -> 1
mysql> SELECT 1 || 0;
        -> 1
mysql> SELECT 0 || 0;
        -> 0
mysql> SELECT 0 || NULL;
        -> NULL
mysql> SELECT 1 || NULL;
        -> 1
```
XOR
Logical XOR. Returns NULL if either operand is NULL. For non-NULL operands, evaluates to 1 if an odd number of operands is non-zero, otherwise 0 is returned.
```
mysql> SELECT 1 XOR 1;
        -> 0
mysql> SELECT 1 XOR 0;
        -> 1
mysql> SELECT 1 XOR NULL;
        -> NULL
mysql> SELECT 1 XOR 1 XOR 1;
        -> 1
```
a XOR b is mathematically equal to (a AND (NOT b)) OR ((NOT a) and b).
XOR was added in MySQL 4.0.2.

12.2. Control Flow Functions

CASE value WHEN [compare_value] THEN result [WHEN [compare_value] THEN result ...] [ELSE result] END
CASE WHEN [condition] THEN result [WHEN [condition] THEN result ...] [ELSE result] END
The first version returns the result where value=compare_value. The second version returns the result for the first condition that is true. If there was no matching result value, the result after ELSE is returned, or NULL if there is no ELSE part.
```
mysql> SELECT CASE 1 WHEN 1 THEN 'one'
    ->     WHEN 2 THEN 'two' ELSE 'more' END;
        -> 'one'
mysql> SELECT CASE WHEN 1>0 THEN 'true' ELSE 'false' END;
        -> 'true'
mysql> SELECT CASE BINARY 'B'
    ->     WHEN 'a' THEN 1 WHEN 'b' THEN 2 END;
        -> NULL
```
Before MySQL 4.1, the type of the return value (INTEGER, DOUBLE, or STRING) is the same as the type of the first returned value (the expression after the first THEN). From MySQL 4.1.0, the default return type is the compatible aggregated type of all return values.
Note that CASE evaluation depends also on the context in which it is used. If used in string context, the result is returned as a string. If used in numeric context, the result is returned decimal, real, or integer value.
CASE was added in MySQL 3.23.3.

IF(expr1,expr2,expr3)

If expr1 is TRUE (expr1 <> 0 and expr1 <> NULL) then IF() returns expr2; otherwise it returns expr3. IF() returns a numeric or string value, depending on the context in which it is used.

mysql> SELECT IF(1>2,2,3);
        -> 3
mysql> SELECT IF(1<2,'yes','no');
        -> 'yes'
mysql> SELECT IF(STRCMP('test','test1'),'no','yes');
        -> 'no'

If only one of expr2 or expr3 is explicitly NULL, the result type of the IF() function is the type of non-NULL expression. (This behavior was implemented in MySQL 4.0.3.)

expr1 is evaluated as an integer value, which means that if you are testing floating-point or string values, you should do so using a comparison operation.

mysql> SELECT IF(0.1,1,0);
        -> 0
mysql> SELECT IF(0.1<>0,1,0);
        -> 1

In the first case shown, IF(0.1) returns 0 because 0.1 is converted to an integer value, resulting in a test of IF(0). This may not be what you expect. In the second case, the comparison tests the original floating-point value to see whether it is non-zero. The result of the comparison is used as an integer.

The default return type of IF() (which may matter when it is stored into a temporary table) is calculated in MySQL 3.23 as follows:

Expression	Return Value
`expr2` or `expr3` returns a string	string
`expr2` or `expr3` returns a floating-point value	floating-point
`expr2` or `expr3` returns an integer	integer

If expr2 and expr3 are both strings, the result is case sensitive if either string is case sensitive (starting from MySQL 3.23.51).

IFNULL(expr1,expr2)
If expr1 is not NULL, IFNULL() returns expr1; otherwise it returns expr2. IFNULL() returns a numeric or string value, depending on the context in which it is used.
```
mysql> SELECT IFNULL(1,0);
        -> 1
mysql> SELECT IFNULL(NULL,10);
        -> 10
mysql> SELECT IFNULL(1/0,10);
        -> 10
mysql> SELECT IFNULL(1/0,'yes');
        -> 'yes'
```
In MySQL 4.0.6 and above, the default result value of IFNULL(expr1,expr2) is the more “general” of the two expressions, in the order STRING, REAL, or INTEGER. The difference from earlier MySQL versions is mostly notable when you create a table based on expressions or MySQL has to internally store a value from IFNULL() in a temporary table.
```
mysql> CREATE TABLE tmp SELECT IFNULL(1,'test') AS test;
mysql> DESCRIBE tmp;
+-------+---------+------+-----+---------+-------+
| Field | Type    | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| test  | char(4) |      |     |         |       |
+-------+---------+------+-----+---------+-------+
```
As of MySQL 4.0.6, the type for the test column is CHAR(4), whereas in earlier versions the type would be BIGINT.
NULLIF(expr1,expr2)
Returns NULL if expr1 = expr2 is true, otherwise returns expr1. This is the same as CASE WHEN expr1 = expr2 THEN NULL ELSE expr1 END.
```
mysql> SELECT NULLIF(1,1);
        -> NULL
mysql> SELECT NULLIF(1,2);
        -> 1
```
Note that MySQL evaluates expr1 twice if the arguments are not equal.
NULLIF() was added in MySQL 3.23.15.

12.3. String Functions

12.3.1. String Comparison Functions

String-valued functions return NULL if the length of the result would be greater than the value of the max_allowed_packet system variable. See Section 7.5.2, “Tuning Server Parameters”.

For functions that operate on string positions, the first position is numbered 1.

ASCII(str)
Returns the numeric value of the leftmost character of the string str. Returns 0 if str is the empty string. Returns NULL if str is NULL. ASCII() works for characters with numeric values from 0 to 255.
```
mysql> SELECT ASCII('2');
        -> 50
mysql> SELECT ASCII(2);
        -> 50
mysql> SELECT ASCII('dx');
        -> 100
```
See also the ORD() function.
BIN(N)
Returns a string representation of the binary value of N, where N is a longlong (BIGINT) number. This is equivalent to CONV(N,10,2). Returns NULL if N is NULL.
```
mysql> SELECT BIN(12);
        -> '1100'
```
BIT_LENGTH(str)
Returns the length of the string str in bits.
```
mysql> SELECT BIT_LENGTH('text');
        -> 32
```
BIT_LENGTH() was added in MySQL 4.0.2.

CHAR(N,... [USING charset_name])

CHAR() interprets each argument N as an integer and returns a string consisting of the characters given by the code values of those integers. NULL values are skipped.

mysql> SELECT CHAR(77,121,83,81,'76');
        -> 'MySQL'
mysql> SELECT CHAR(77,77.3,'77.3');
        -> 'MMM'

CHAR() returns a string in the connection character set. As of MySQL 4.1.16, the optional USING clause may be used to produce a string in a given character set:

mysql> SELECT CHARSET(CHAR(0x65)), CHARSET(CHAR(0x65 USING utf8));
+---------------------+--------------------------------+
| CHARSET(CHAR(0x65)) | CHARSET(CHAR(0x65 USING utf8)) |
+---------------------+--------------------------------+
| latin1              | utf8                           |
+---------------------+--------------------------------+

CHAR_LENGTH(str)
Returns the length of the string str, measured in characters. A multi-byte character counts as a single character. This means that for a string containing five two-byte characters, LENGTH() returns 10, whereas CHAR_LENGTH() returns 5.
CHARACTER_LENGTH(str)
CHARACTER_LENGTH() is a synonym for CHAR_LENGTH().
CONCAT(str1,str2,...)
Returns the string that results from concatenating the arguments. May have one or more arguments. If all arguments are non-binary strings, the result is a non-binary string. If the arguments include any binary strings, the result is a binary string. A numeric argument is converted to its equivalent binary string form; if you want to avoid that, you can use an explicit type cast, as in this example:
```
SELECT CONCAT(CAST(int_col AS CHAR), char_col);
```
CONCAT() returns NULL if any argument is NULL.
```
mysql> SELECT CONCAT('My', 'S', 'QL');
        -> 'MySQL'
mysql> SELECT CONCAT('My', NULL, 'QL');
        -> NULL
mysql> SELECT CONCAT(14.3);
        -> '14.3'
```
CONCAT_WS(separator,str1,str2,...)
CONCAT_WS() stands for Concatenate With Separator and is a special form of CONCAT(). The first argument is the separator for the rest of the arguments. The separator is added between the strings to be concatenated. The separator can be a string, as can the rest of the arguments. If the separator is NULL, the result is NULL.
```
mysql> SELECT CONCAT_WS(',','First name','Second name','Last Name');
        -> 'First name,Second name,Last Name'
mysql> SELECT CONCAT_WS(',','First name',NULL,'Last Name');
        -> 'First name,Last Name'
```
CONCAT_WS() skips any NULL values after the separator argument. Before MySQL 4.0.14, CONCAT_WS() skips empty strings as well as NULL values.
CONV(N,from_base,to_base)
Converts numbers between different number bases. Returns a string representation of the number N, converted from base from_base to base to_base. Returns NULL if any argument is NULL. The argument N is interpreted as an integer, but may be specified as an integer or a string. The minimum base is 2 and the maximum base is 36. If to_base is a negative number, N is regarded as a signed number. Otherwise, N is treated as unsigned. CONV() works with 64-bit precision.
```
mysql> SELECT CONV('a',16,2);
        -> '1010'
mysql> SELECT CONV('6E',18,8);
        -> '172'
mysql> SELECT CONV(-17,10,-18);
        -> '-H'
mysql> SELECT CONV(10+'10'+'10'+0xa,10,10);
        -> '40'
```
ELT(N,str1,str2,str3,...)
Returns str1 if N = 1, str2 if N = 2, and so on. Returns NULL if N is less than 1 or greater than the number of arguments. ELT() is the complement of FIELD().
```
mysql> SELECT ELT(1, 'ej', 'Heja', 'hej', 'foo');
        -> 'ej'
mysql> SELECT ELT(4, 'ej', 'Heja', 'hej', 'foo');
        -> 'foo'
```
EXPORT_SET(bits,on,off[,separator[,number_of_bits]])
Returns a string such that for every bit set in the value bits, you get an on string and for every reset bit, you get an off string. Bits in bits are examined from right to left (from low-order to high-order bits). Strings are added to the result from left to right, separated by the separator string (the default being the comma character ‘,’). The number of bits examined is given by number_of_bits (defaults to 64).
```
mysql> SELECT EXPORT_SET(5,'Y','N',',',4);
        -> 'Y,N,Y,N'
mysql> SELECT EXPORT_SET(6,'1','0',',',10);
        -> '0,1,1,0,0,0,0,0,0,0'
```
FIELD(str,str1,str2,str3,...)
Returns the index (position) of str in the str1, str2, str3, ... list. Returns 0 if str is not found.
If all arguments to FIELD() are strings, all arguments are compared as strings. If all arguments are numbers, they are compared as numbers. Otherwise, the arguments are compared as double.
If str is NULL, the return value is 0 because NULL fails equality comparison with any value. FIELD() is the complement of ELT().
```
mysql> SELECT FIELD('ej', 'Hej', 'ej', 'Heja', 'hej', 'foo');
        -> 2
mysql> SELECT FIELD('fo', 'Hej', 'ej', 'Heja', 'hej', 'foo');
        -> 0
```
FIND_IN_SET(str,strlist)
Returns a value in the range of 1 to N if the string str is in the string list strlist consisting of N substrings. A string list is a string composed of substrings separated by ‘,’ characters. If the first argument is a constant string and the second is a column of type SET, the FIND_IN_SET() function is optimized to use bit arithmetic. Returns 0 if str is not in strlist or if strlist is the empty string. Returns NULL if either argument is NULL. This function does not work properly if the first argument contains a comma (‘,’) character.
```
mysql> SELECT FIND_IN_SET('b','a,b,c,d');
        -> 2
```

FORMAT(X,D)

Formats the number X to a format like '#,###,###.##', rounded to D decimal places, and returns the result as a string. If D is 0, the result has no decimal point or fractional part.

mysql> SELECT FORMAT(12332.123456, 4);
        -> '12,332.1235'
mysql> SELECT FORMAT(12332.1,4);
        -> '12,332.1000'
mysql> SELECT FORMAT(12332.2,0);
        -> '12,332'

HEX(N_or_S)
If N_or_S is a number, returns a string representation of the hexadecimal value of N, where N is a longlong (BIGINT) number. This is equivalent to CONV(N,10,16).
From MySQL 4.0.1 and up, if N_or_S is a string, returns a hexadecimal string representation of N_or_S where each character in N_or_S is converted to two hexadecimal digits.
```
mysql> SELECT HEX(255);
        -> 'FF'
mysql> SELECT 0x616263;
        -> 'abc'
mysql> SELECT HEX('abc');
        -> 616263
```
INSERT(str,pos,len,newstr)
Returns the string str, with the substring beginning at position pos and len characters long replaced by the string newstr. Returns the original string if pos is not within the length of the string. Replaces the rest of the string from position pos is len is not within the length of the rest of the string. Returns NULL if any argument is NULL.
```
mysql> SELECT INSERT('Quadratic', 3, 4, 'What');
        -> 'QuWhattic'
mysql> SELECT INSERT('Quadratic', -1, 4, 'What');
        -> 'Quadratic'
mysql> SELECT INSERT('Quadratic', 3, 100, 'What');
        -> 'QuWhat'
```
This function is multi-byte safe.
INSTR(str,substr)
Returns the position of the first occurrence of substring substr in string str. This is the same as the two-argument form of LOCATE(), except that the order of the arguments is reversed.
```
mysql> SELECT INSTR('foobarbar', 'bar');
        -> 4
mysql> SELECT INSTR('xbar', 'foobar');
        -> 0
```
This function is multi-byte safe. In MySQL 3.23, this function is case sensitive. For 4.0 on, it is case sensitive only if either argument is a binary string.
LCASE(str)
LCASE() is a synonym for LOWER().

LEFT(str,len)

Returns the leftmost len characters from the string str.

mysql> SELECT LEFT('foobarbar', 5);
        -> 'fooba'

LENGTH(str)
Returns the length of the string str, measured in bytes. A multi-byte character counts as multiple bytes. This means that for a string containing five two-byte characters, LENGTH() returns 10, whereas CHAR_LENGTH() returns 5.
```
mysql> SELECT LENGTH('text');
        -> 4
```
LOAD_FILE(file_name)
Reads the file and returns the file contents as a string. To use this function, the file must be located on the server host, you must specify the full pathname to the file, and you must have the FILE privilege. The file must be readable by all and its size less than max_allowed_packet bytes.
If the file does not exist or cannot be read because one of the preceding conditions is not satisfied, the function returns NULL.
```
mysql> UPDATE t
            SET blob_col=LOAD_FILE('/tmp/picture')
            WHERE id=1;
```
Before MySQL 3.23, you must read the file inside your application and create an INSERT statement to update the database with the file contents. If you are using the MySQL++ library, one way to do this can be found in the MySQL++ manual, available at http://tangentsoft.net/mysql++/doc/.
LOCATE(substr,str), LOCATE(substr,str,pos)
The first syntax returns the position of the first occurrence of substring substr in string str. The second syntax returns the position of the first occurrence of substring substr in string str, starting at position pos. Returns 0 if substr is not in str.
```
mysql> SELECT LOCATE('bar', 'foobarbar');
        -> 4
mysql> SELECT LOCATE('xbar', 'foobar');
        -> 0
mysql> SELECT LOCATE('bar', 'foobarbar', 5);
        -> 7
```
This function is multi-byte safe. In MySQL 3.23, this function is case sensitive. For 4.0 on, it is case sensitive only if either argument is a binary string.
LOWER(str)
Returns the string str with all characters changed to lowercase according to the current character set mapping. The default is latin1 (cp1252 West European).
```
mysql> SELECT LOWER('QUADRATICALLY');
        -> 'quadratically'
```
This function is multi-byte safe.
LPAD(str,len,padstr)
Returns the string str, left-padded with the string padstr to a length of len characters. If str is longer than len, the return value is shortened to len characters.
```
mysql> SELECT LPAD('hi',4,'??');
        -> '??hi'
mysql> SELECT LPAD('hi',1,'??');
        -> 'h'
```
LTRIM(str)
Returns the string str with leading space characters removed.
```
mysql> SELECT LTRIM('  barbar');
        -> 'barbar'
```
This function is multi-byte safe.

MAKE_SET(bits,str1,str2,...)

Returns a set value (a string containing substrings separated by ‘,’ characters) consisting of the strings that have the corresponding bit in bits set. str1 corresponds to bit 0, str2 to bit 1, and so on. NULL values in str1, str2, ... are not appended to the result.

mysql> SELECT MAKE_SET(1,'a','b','c');
        -> 'a'
mysql> SELECT MAKE_SET(1 | 4,'hello','nice','world');
        -> 'hello,world'
mysql> SELECT MAKE_SET(1 | 4,'hello','nice',NULL,'world');
        -> 'hello'
mysql> SELECT MAKE_SET(0,'a','b','c');
        -> ''

MID(str,pos,len)
MID(str,pos,len) is a synonym for SUBSTRING(str,pos,len).
OCT(N)
Returns a string representation of the octal value of N, where N is a longlong (BIGINT) number. This is equivalent to CONV(N,10,8). Returns NULL if N is NULL.
```
mysql> SELECT OCT(12);
        -> '14'
```
OCTET_LENGTH(str)
OCTET_LENGTH() is a synonym for LENGTH().
ORD(str)
If the leftmost character of the string str is a multi-byte character, returns the code for that character, calculated from the numeric values of its constituent bytes using this formula:
```
  (1st byte code)
+ (2nd byte code × 256)
+ (3rd byte code × 256²) ...
```
If the leftmost character is not a multi-byte character, ORD() returns the same value as the ASCII() function.
```
mysql> SELECT ORD('2');
        -> 50
```
POSITION(substr IN str)
POSITION(substr IN str) is a synonym for LOCATE(substr,str).
QUOTE(str)
Quotes a string to produce a result that can be used as a properly escaped data value in an SQL statement. The string is returned enclosed by single quotes and with each instance of single quote (‘'’), backslash (‘\’), ASCII NUL, and Control-Z preceded by a backslash. If the argument is NULL, the return value is the word “NULL” without enclosing single quotes. The QUOTE() function was added in MySQL 4.0.3.
```
mysql> SELECT QUOTE('Don\'t!');
        -> 'Don\'t!'
mysql> SELECT QUOTE(NULL);
        -> NULL
```
REPEAT(str,count)
Returns a string consisting of the string str repeated count times. If count is less than 1, returns an empty string. Returns NULL if str or count are NULL.
```
mysql> SELECT REPEAT('MySQL', 3);
        -> 'MySQLMySQLMySQL'
```
REPLACE(str,from_str,to_str)
Returns the string str with all occurrences of the string from_str replaced by the string to_str. REPLACE() performs a case-sensitive match when searching for from_str.
```
mysql> SELECT REPLACE('www.mysql.com', 'w', 'Ww');
        -> 'WwWwWw.mysql.com'
```
This function is multi-byte safe.
REVERSE(str)
Returns the string str with the order of the characters reversed.
```
mysql> SELECT REVERSE('abc');
        -> 'cba'
```
This function is multi-byte safe.
RIGHT(str,len)
Returns the rightmost len characters from the string str.
```
mysql> SELECT RIGHT('foobarbar', 4);
        -> 'rbar'
```
This function is multi-byte safe.
RPAD(str,len,padstr)
Returns the string str, right-padded with the string padstr to a length of len characters. If str is longer than len, the return value is shortened to len characters.
```
mysql> SELECT RPAD('hi',5,'?');
        -> 'hi???'
mysql> SELECT RPAD('hi',1,'?');
        -> 'h'
```
This function is multi-byte safe.
RTRIM(str)
Returns the string str with trailing space characters removed.
```
mysql> SELECT RTRIM('barbar   ');
        -> 'barbar'
```
This function is multi-byte safe.
SOUNDEX(str)
Returns a soundex string from str. Two strings that sound almost the same should have identical soundex strings. A standard soundex string is four characters long, but the SOUNDEX() function returns an arbitrarily long string. You can use SUBSTRING() on the result to get a standard soundex string. All non-alphabetic characters in str are ignored. All international alphabetic characters outside the A-Z range are treated as vowels.
```
mysql> SELECT SOUNDEX('Hello');
        -> 'H400'
mysql> SELECT SOUNDEX('Quadratically');
        -> 'Q36324'
```
Note: This function implements the original Soundex algorithm, not the more popular enhanced version (also described by D. Knuth). The difference is that original version discards vowels first and duplicates second, whereas the enhanced version discards duplicates first and vowels second.
expr1 SOUNDS LIKE expr2
This is the same as SOUNDEX(expr1) = SOUNDEX(expr2). It is available beginning with MySQL 4.1.0.
SPACE(N)
Returns a string consisting of N space characters.
```
mysql> SELECT SPACE(6);
        -> '      '
```
SUBSTRING(str,pos), SUBSTRING(str FROM pos), SUBSTRING(str,pos,len), SUBSTRING(str FROM pos FOR len)
The forms without a len argument return a substring from string str starting at position pos. The forms with a len argument return a substring len characters long from string str, starting at position pos. The forms that use FROM are standard SQL syntax. Beginning with MySQL 4.1.0, it is possible to use a negative value for pos. In this case, the beginning of the substring is pos characters from the end of the string, rather than the beginning. A negative value may be used for pos in any of the forms of this function.
```
mysql> SELECT SUBSTRING('Quadratically',5);
        -> 'ratically'
mysql> SELECT SUBSTRING('foobarbar' FROM 4);
        -> 'barbar'
mysql> SELECT SUBSTRING('Quadratically',5,6);
        -> 'ratica'        
mysql> SELECT SUBSTRING('Sakila', -3);
        -> 'ila'        
mysql> SELECT SUBSTRING('Sakila', -5, 3);
        -> 'aki'
mysql> SELECT SUBSTRING('Sakila' FROM -4 FOR 2);
        -> 'ki'
```
This function is multi-byte safe.
If len is less than 1, the result is the empty string.
SUBSTR() is a synonym for SUBSTRING(), added in MySQL 4.1.1.
SUBSTRING_INDEX(str,delim,count)
Returns the substring from string str before count occurrences of the delimiter delim. If count is positive, everything to the left of the final delimiter (counting from the left) is returned. If count is negative, everything to the right of the final delimiter (counting from the right) is returned. SUBSTRING_INDEX() performs a case-sensitive match when searching for delim.
```
mysql> SELECT SUBSTRING_INDEX('www.mysql.com', '.', 2);
        -> 'www.mysql'
mysql> SELECT SUBSTRING_INDEX('www.mysql.com', '.', -2);
        -> 'mysql.com'
```
This function is multi-byte safe.
TRIM([{BOTH | LEADING | TRAILING} [remstr] FROM] str), TRIM([remstr FROM] str)
Returns the string str with all remstr prefixes or suffixes removed. If none of the specifiers BOTH, LEADING, or TRAILING is given, BOTH is assumed. remstr is optional and, if not specified, spaces are removed.
```
mysql> SELECT TRIM('  bar   ');
        -> 'bar'
mysql> SELECT TRIM(LEADING 'x' FROM 'xxxbarxxx');
        -> 'barxxx'
mysql> SELECT TRIM(BOTH 'x' FROM 'xxxbarxxx');
        -> 'bar'
mysql> SELECT TRIM(TRAILING 'xyz' FROM 'barxxyz');
        -> 'barx'
```
This function is multi-byte safe.
UCASE(str)
UCASE() is a synonym for UPPER().
UNHEX(str)
Performs the inverse operation of HEX(str). That is, it interprets each pair of hexadecimal digits in the argument as a number and converts it to the character represented by the number. The resulting characters are returned as a binary string.
```
mysql> SELECT UNHEX('4D7953514C');
        -> 'MySQL'
mysql> SELECT 0x4D7953514C;
        -> 'MySQL'
mysql> SELECT UNHEX(HEX('string'));
        -> 'string'
mysql> SELECT HEX(UNHEX('1267'));
        -> '1267'
```
UNHEX() was added in MySQL 4.1.2.
UPPER(str)
Returns the string str with all characters changed to uppercase according to the current character set mapping. The default is latin1 (cp1252 West European).
```
mysql> SELECT UPPER('Hej');
        -> 'HEJ'
```
This function is multi-byte safe.

12.3.1. String Comparison Functions

If a string function is given a binary string as an argument, the resulting string is also a binary string. A number converted to a string is treated as a binary string. This affects only comparisons.

Normally, if any expression in a string comparison is case sensitive, the comparison is performed in case-sensitive fashion.

expr LIKE pat [ESCAPE 'escape_char']
Pattern matching using SQL simple regular expression comparison. Returns 1 (TRUE) or 0 (FALSE). If either expr or pat is NULL, the result is NULL.
The pattern need not be a literal string. For example, it can be specified as a string expression or table column.
Per the SQL standard, LIKE performs matching on a per-character basis, thus it can produce results different from the = comparison operator:
```
mysql> SELECT 'ä' LIKE 'ae' COLLATE latin1_german2_ci;
+-----------------------------------------+
| 'ä' LIKE 'ae' COLLATE latin1_german2_ci |
+-----------------------------------------+
|                                       0 |
+-----------------------------------------+
mysql> SELECT 'ä' = 'ae' COLLATE latin1_german2_ci;
+--------------------------------------+
| 'ä' = 'ae' COLLATE latin1_german2_ci |
+--------------------------------------+
|                                    1 |
+--------------------------------------+
```
With LIKE you can use the following two wildcard characters in the pattern:
Character Description
% Matches any number of characters, even zero characters
_ Matches exactly one character
```
mysql> SELECT 'David!' LIKE 'David_';
        -> 1
mysql> SELECT 'David!' LIKE '%D%v%';
        -> 1
```
To test for literal instances of a wildcard character, precede it by the escape character. If you do not specify the ESCAPE character, ‘\’ is assumed.
String Description
\% Matches one ‘%’ character
\_ Matches one ‘_’ character
```
mysql> SELECT 'David!' LIKE 'David\_';
        -> 0
mysql> SELECT 'David_' LIKE 'David\_';
        -> 1
```
To specify a different escape character, use the ESCAPE clause:
```
mysql> SELECT 'David_' LIKE 'David|_' ESCAPE '|';
        -> 1
```
The following two statements illustrate that string comparisons are not case sensitive unless one of the operands is a binary string:
```
mysql> SELECT 'abc' LIKE 'ABC';
        -> 1
mysql> SELECT 'abc' LIKE BINARY 'ABC';
        -> 0
```
In MySQL, LIKE is allowed on numeric expressions. (This is an extension to the standard SQL LIKE.)
```
mysql> SELECT 10 LIKE '1%';
        -> 1
```
Note: Because MySQL uses C escape syntax in strings (for example, ‘\n’ to represent a newline character), you must double any ‘\’ that you use in LIKE strings. For example, to search for ‘\n’, specify it as ‘\\n’. To search for ‘\’, specify it as ‘\\\\’; this is because the backslashes are stripped once by the parser and again when the pattern match is made, leaving a single backslash to be matched against. (Exception: At the end of the pattern string, backslash can be specified as ‘\\’. At the end of the string, backslash stands for itself because there is nothing following to escape.)
expr NOT LIKE pat [ESCAPE 'escape_char']
This is the same as NOT (expr LIKE pat [ESCAPE 'escape_char']).
expr NOT REGEXP pat, expr NOT RLIKE pat
This is the same as NOT (expr REGEXP pat).
expr REGEXP pat expr RLIKE pat
Performs a pattern match of a string expression expr against a pattern pat. The pattern can be an extended regular expression. The syntax for regular expressions is discussed in Appendix G, Regular Expressions. Returns 1 if expr matches pat; otherwise it returns 0. If either expr or pat is NULL, the result is NULL. RLIKE is a synonym for REGEXP, provided for mSQL compatibility.
The pattern need not be a literal string. For example, it can be specified as a string expression or table column.
Note: Because MySQL uses the C escape syntax in strings (for example, ‘\n’ to represent the newline character), you must double any ‘\’ that you use in your REGEXP strings.
As of MySQL 3.23.4, REGEXP is not case sensitive, except when used with binary strings.
```
mysql> SELECT 'Monty!' REGEXP 'm%y%%';
        -> 0
mysql> SELECT 'Monty!' REGEXP '.*';
        -> 1
mysql> SELECT 'new*\n*line' REGEXP 'new\\*.\\*line';
        -> 1
mysql> SELECT 'a' REGEXP 'A', 'a' REGEXP BINARY 'A';
        -> 1  0
mysql> SELECT 'a' REGEXP '^[a-d]';
        -> 1
```
REGEXP and RLIKE use the current character set when deciding the type of a character. The default is latin1 (cp1252 West European). Warning: These operators are not multi-byte safe.
STRCMP(expr1,expr2)
STRCMP() returns 0 if the strings are the same, -1 if the first argument is smaller than the second according to the current sort order, and 1 otherwise.
```
mysql> SELECT STRCMP('text', 'text2');
        -> -1
mysql> SELECT STRCMP('text2', 'text');
        -> 1
mysql> SELECT STRCMP('text', 'text');
        -> 0
```
As of MySQL 4.0, STRCMP() uses the current character set when performing comparisons. This makes the default comparison behavior case insensitive unless one or both of the operands are binary strings. Before MySQL 4.0, STRCMP() is case sensitive.

12.4. Numeric Functions

12.4.1. Arithmetic Operators
12.4.2. Mathematical Functions

12.4.1. Arithmetic Operators

The usual arithmetic operators are available. The precision of the result is determined according to the following rules:

Note that in the case of -, +, and *, the result is calculated with BIGINT (64-bit) precision if both arguments are integers.
If one of the arguments is an unsigned integer, and the other argument is also an integer, the result is an unsigned integer.
If any of the operands of a +, -, /, *, % is a real or string value, then the precision of the result is the precision of the argument with the maximum precision.
In multiplication and division, the precision of the result when using two integer values is the precision of the first argument + the value of the div_precision_increment global variable. For example, the expression 5.05 / 0.0014 would have a precision of six decimal places (4.047976).

These rules are applied for each operation, such that nested calculations imply the precision of each component. Hence, (14620 / 9432456) / (24250 / 9432456), would resolve first to (0.0014) / (0.0026), with the final result having 8 decimal places (0.57692308).

Because of these rules and the method they are applied, care should be taken to ensure that components and sub-components of a calculation use the appropriate level of precision. See Section 12.8, “Cast Functions and Operators”.

+
Addition:
```
mysql> SELECT 3+5;
        -> 8
```
-
Subtraction:
```
mysql> SELECT 3-5;
        -> -2
```
-
Unary minus. This operator changes the sign of the argument.
```
mysql> SELECT - 2;
        -> -2
```
Note: If this operator is used with a BIGINT, the return value is also a BIGINT. This means that you should avoid using – on integers that may have the value of –2⁶³.

*

Multiplication:

mysql> SELECT 3*5;
        -> 15
mysql> SELECT 18014398509481984*18014398509481984.0;
        -> 324518553658426726783156020576256.0
mysql> SELECT 18014398509481984*18014398509481984;
        -> 0

The result of the last expression is incorrect because the result of the integer multiplication exceeds the 64-bit range of BIGINT calculations. (See Section 11.2, “Numeric Types”.)

/
Division:
```
mysql> SELECT 3/5;
        -> 0.60
```
Division by zero produces a NULL result:
```
mysql> SELECT 102/(1-1);
        -> NULL
```
A division is calculated with BIGINT arithmetic only if performed in a context where its result is converted to an integer.
DIV
Integer division. Similar to FLOOR(), but is safe with BIGINT values.
```
mysql> SELECT 5 DIV 2;
        -> 2
```
DIV was implemented in MySQL 4.1.0.

12.4.2. Mathematical Functions

All mathematical functions return NULL in the event of an error.

ABS(X)

Returns the absolute value of X.

mysql> SELECT ABS(2);
        -> 2
mysql> SELECT ABS(-32);
        -> 32

This function is safe to use with BIGINT values.

ACOS(X)

Returns the arc cosine of X, that is, the value whose cosine is X. Returns NULL if X is not in the range -1 to 1.

mysql> SELECT ACOS(1);
        -> 0.000000
mysql> SELECT ACOS(1.0001);
        -> NULL
mysql> SELECT ACOS(0);
        -> 1.570796

ASIN(X)
Returns the arc sine of X, that is, the value whose sine is X. Returns NULL if X is not in the range -1 to 1.
```
mysql> SELECT ASIN(0.2);
        -> 0.201358
mysql> SELECT ASIN('foo');
        -> 0.000000
```

ATAN(X)

Returns the arc tangent of X, that is, the value whose tangent is X.

mysql> SELECT ATAN(2);
        -> 1.107149
mysql> SELECT ATAN(-2);
        -> -1.107149

ATAN(Y,X), ATAN2(Y,X)
Returns the arc tangent of the two variables X and Y. It is similar to calculating the arc tangent of Y / X, except that the signs of both arguments are used to determine the quadrant of the result.
```
mysql> SELECT ATAN(-2,2);
        -> -0.785398
mysql> SELECT ATAN2(PI(),0);
        -> 1.570796
```
CEILING(X), CEIL(X)
Returns the smallest integer value not less than X.
```
mysql> SELECT CEILING(1.23);
        -> 2
mysql> SELECT CEIL(-1.23);
        -> -1
```
Note that the return value is converted to a BIGINT.
The CEIL()