=

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

For row comparisons, (a, b) = (x, y) is equivalent to:

(a = x) AND (b = y)

<=>

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.

The <=> operator is equivalent to the standard SQL IS NOT DISTINCT FROM operator.

mysql> SELECT 1 <=> 1, NULL <=> NULL, 1 <=> NULL;
        -> 1, 1, 0
mysql> SELECT 1 = 1, NULL = NULL, 1 = NULL;
        -> 1, NULL, NULL

For row comparisons, (a, b) <=> (x, y) is equivalent to:

(a <=> x) AND (b <=> y)

<>, !=

Not equal:

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

For row comparisons, (a, b) <> (x, y) and (a, b) != (x, y) are equivalent to:

(a <> x) OR (b <> y)

<=

Less than or equal:

mysql> SELECT 0.1 <= 2;
        -> 1

For row comparisons, (a, b) <= (x, y) is equivalent to:

(a < x) OR ((a = x) AND (b <= y))

<

Less than:

mysql> SELECT 2 < 2;
        -> 0

For row comparisons, (a, b) < (x, y) is equivalent to:

(a < x) OR ((a = x) AND (b < y))

>=

Greater than or equal:

mysql> SELECT 2 >= 2;
        -> 1

For row comparisons, (a, b) >= (x, y) is equivalent to:

(a > x) OR ((a = x) AND (b >= y))

>

Greater than:

mysql> SELECT 2 > 2;
        -> 0

For row comparisons, (a, b) > (x, y) is equivalent to:

(a > x) OR ((a = x) AND (b > y))

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 12.3, “Type Conversion in Expression Evaluation”, but applied to all the three arguments.

mysql> SELECT 2 BETWEEN 1 AND 3, 2 BETWEEN 3 and 1;
        -> 1, 0
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

For best results when using BETWEEN with date or time values, use CAST() to explicitly convert the values to the desired data type. Examples: If you compare a DATETIME to two DATE values, convert the DATE values to DATETIME values. If you use a string constant such as '2001-1-1' in a comparison to a DATE, cast the string to a DATE.

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.

The return type of COALESCE() is the aggregated type of the argument types.

mysql> SELECT COALESCE(NULL,1);
        -> 1
mysql> SELECT COALESCE(NULL,NULL,NULL);
        -> NULL

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 if any argument is NULL.

expr IN (value,...)

Returns 1 (true) if expr is equal to any of the values in the IN() list, else returns 0 (false).

Type conversion takes place according to the rules described in Section 12.3, “Type Conversion in Expression Evaluation”, applied to all the arguments. If no type conversion is needed for the values in the IN() list, they are all constants of the same type, and expr can be compared to each of them as a value of the same type (possibly after type conversion), an optimization takes place. The values the list are sorted and the search for expr is done using a binary search, which makes the IN() operation very quick.

mysql> SELECT 2 IN (0,3,5,7);
        -> 0
mysql> SELECT 'wefwf' IN ('wee','wefwf','weg');
        -> 1

IN() can be used to compare row constructors:

mysql> SELECT (3,4) IN ((1,2), (3,4));
        -> 1
mysql> SELECT (3,4) IN ((1,2), (3,5));
        -> 0

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');

Implicit type conversion may produce nonintuitive results:

mysql> SELECT 'a' IN (0), 0 IN ('b');
        -> 1, 1

In both cases, the comparison values are converted to floating-point values, yielding 0.0 in each case, and a comparison result of 1 (true).

The number of values in the IN() list is only limited by the max_allowed_packet value.

To comply with the SQL standard, 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.

IN() syntax can also be used to write certain types of subqueries. See Section 13.2.10.3, “Subqueries with ANY, IN, or SOME”.

expr NOT IN (value,...)

This is the same as NOT (expr IN (value,...)).

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

IS boolean_value

Tests a value against a boolean value, where boolean_value can be TRUE, FALSE, or UNKNOWN.

mysql> SELECT 1 IS TRUE, 0 IS FALSE, NULL IS UNKNOWN;
        -> 1, 1, 1

IS NOT boolean_value

Tests a value against a boolean value, where boolean_value can be TRUE, FALSE, or UNKNOWN.

mysql> SELECT 1 IS NOT UNKNOWN, 0 IS NOT UNKNOWN, NULL IS NOT UNKNOWN;
        -> 1, 1, 0

IS NULL

Tests whether a value is NULL.

mysql> SELECT 1 IS NULL, 0 IS NULL, NULL IS NULL;
        -> 0, 0, 1

To work well with ODBC programs, MySQL supports the following extra features when using IS NULL:

IS NOT NULL

Tests whether a value is not NULL.

mysql> SELECT 1 IS NOT NULL, 0 IS NOT NULL, NULL IS NOT NULL;
        -> 1, 1, 0

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 NULL.)

The ISNULL() function shares some special behaviors with the IS NULL comparison operator. See the description of IS NULL.

LEAST(value1,value2,...)

With two or more arguments, returns the smallest (minimum-valued) argument. The arguments are compared using the following rules:

The return type of LEAST() is the aggregated type of the comparison argument types.

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'