Table of Contents [+/-]
Expressions can be used at several points in SQL statements, such as
ORDER BY or
SELECT statements, in the
WHERE clause of a
UPDATE statement, or in
statements. Expressions can be written using literal values, column
NULL, built-in functions, stored
functions, user-defined functions, and operators. This chapter
describes the functions and operators that are permitted for writing
expressions in MySQL. Instructions for writing stored functions and
user-defined functions are given in
Section 18.2, “Using Stored Routines (Procedures and Functions)”, and
Section 21.2, “Adding New Functions to MySQL”. See
Section 9.2.3, “Function Name Parsing and Resolution”, for the rules describing how
the server interprets references to different kinds of functions.
An expression that contains
NULL always produces
NULL value unless otherwise indicated in the
documentation for a particular function or operator.
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 5.1.7, “Server SQL Modes”.) Individual client programs can request
this behavior by using the
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:
SELECT MOD(29,9);+-----------+ | mod(29,9) | +-----------+ | 2 | +-----------+ 1 rows in set (0.00 sec)
This format is used instead:
SELECT MOD(29,9);-> 2