Chapter 12. Functions and Operators
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, stored functions, user-defined functions, and
operators. This chapter describes the functions and operators that
are allowed for writing expressions in MySQL. Instructions for
writing stored functions and user-defined functions are given in
Chapter 19, Stored Procedures and Functions, and
Section 27.3, “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
