Page 421 - Beginning PHP 5.3

Chapter 13: Retrieving Data from MySQL with PHP
Much like PHP, MySQL features various comparison operators that you can use to compare column
values and other expressions in your queries. Here are some common ones:

Comparison Operator Description
= equal to

< = > NULL - safe version of equal
to
!= or < > not equal to

< less than
> greater than
< = less than or equal to

> = greater than or equal to

Using a comparison operator results in a value of 1 ( TRUE ), 0 ( FALSE ), or NULL .

Most of these operators are self - explanatory. < = > is useful if you think either of the values you ’ re
comparing might be NULL . Remember that NULL values propagate throughout an expression, so if any
value in an expression is NULL , the result will also be NULL . This isn ’ t very helpful when you ’ re trying to
compare two values. For example:

mysql > select 1 = 2;
+-------+
| 1 = 2 |
+-------+
| 0 |
+-------+
1 row in set (0.00 sec)

mysql > select 2 = 2;
+-------+
| 2 = 2 |
+-------+
| 1 |
+-------+
1 row in set (0.00 sec)

mysql > select 1 = NULL;
+----------+
| 1 = NULL |
+----------+
| NULL |
+----------+

1 row in set (0.00 sec)

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