=======  Comparison Functions ======

Comparison operators return 1 (TRUE), 0 (FALSE) or NULL values. These functions work with both numbers and strings. Strings, if required, are converted automatically to numbers, and vice versa. 

Comparison operators of SQL work according to the following rules:
  * If one or both arguments is NULL then the result is also NULL. 
  * If both arguments are strings then they are compared as strings.
  * If both arguments are integer numbers then they are compared as integers.
  * In all other cases arguments are compared as real numbers. 

<code sql>
SELECT IF( 1 > 2, 1, 0 );
=> 0
SELECT IF( 2 > 1, 1, 0 );
=> 1
SELECT IF( 'aa' > 'aa', 1, 0 );
=> 0
SELECT IF( 'ab' > 'aa', 1, 0 );
=> 1
</code>




===== Operator '=' =====

Operator Equal.

<code sql>
SELECT IF( 1 = 0, 1, 0 );
=> 0
SELECT IF( '0' = 0, 1, 0 );
=> 1
SELECT IF( '0.0' = 0, 1, 0 );
=> 1
SELECT IF( '0.01' = 0, 1, 0 );
=> 0
SELECT IF( '.01' = 0.01, 1, 0 );
=> 1
</code>



===== Operator '<>' / '!=' =====

Operator Not Equal.

2 forms are supported:
**<>** - SQL Standard
**!=** - C syntax

<code sql>
SELECT IF( '.01' <> '0.01', 1, 0 );
=> 1
SELECT IF( .01 <> '0.01', 1, 0 );
=> 0
SELECT IF( 'zapp' <> 'zappp', 1, 0 );
=> 1
</code>


===== Operator '<=' =====

Operator Less Than Or Equal.
 
<code sql>
SELECT IF( 0.1 <= 2, 1, 0 );
=> 1
</code>


===== Operator '<' =====

Operator Less Than.

<code sql>
SELECT IF( 2 < 2, 1, 0 );
=> 0
</code>



===== Operator '>=' =====

Operator Greater Than Or Equal.

<code sql>
SELECT IF( 2 >= 2, 1, 0 );
=> 1
</code>


===== Operator '>' =====
 
Operator Greater Than.

<code sql>
SELECT IF( 2 > 2, 1, 0 );
=> 0
</code>
 


===== Operator BETWEEN =====

**expr BETWEEN min AND max**

This operator is equivalent to the expression (min <= expr AND expr <= max) that has all arguments of the same type. Otherwise type conversions will  be performed as described above.

<code sql>
SELECT IF( 1 BETWEEN 2 AND 3, 1, 0 );
=> 0
SELECT IF( 'b' BETWEEN 'a' AND 'c', 1, 0 );
=> 1
SELECT IF( 2 BETWEEN 2 AND '3', 1, 0 );
=> 1
</code>

\\
**expr NOT BETWEEN min AND max** 

Equivalent to NOT (expr BETWEEN min AND max). 



===== Operator IN =====

**expr IN (value,...)**

Returns 1 if the expression EXPR is equal to any value from the list IN, otherwise returns 0. 

Note: if all values are constants, then they are sorted according to type. The search in this case is done with use of a Binary search, i.e. very fast.

<code sql>
SELECT IF( 2 IN (0,3,5,'wefwf'), 1, 0 );
=> 0
SELECT IF( 'wefwf' IN (0,3,5,'wefwf'), 1, 0 );
=> 1
</code>

**expr NOT IN (value,...)**

Equivalent to NOT (expr IN (value,...)). 



===== Operator IS NULL =====

**IS [NOT] NULL**

Tests if a value is NULL.

<code sql>
SELECT IF(1 IS NULL, 1, 0), IF(0 IS NULL, 1, 0 ), IF(NULL IS NULL, 1, 0 );
=> 0 0 1
SELECT IF(1 IS NOT NULL, 1, 0), IF(0 IS NOT NULL, 1, 0 ), IF(NULL IS NOT NULL, 1, 0);
=> 1 1 0
</code>





===== Function ISNULL() =====

**ISNULL(expression_value, replacement_value)**

Returns replacement value if expression value is NULL, otherwise returns expression value.

<code sql>
SELECT ISNULL(2+2, 1);
=> 4
SELECT ISNULL(1/0, 1);
=> 1
</code>

Note: comparison of NULL values by operator = always will return FALSE.

<code sql>
SELECT IF( NULL = NULL, 1, 0 );
=> 0
</code>