Expressions can be used at several points inSQL statements, such as in theORDER BY orHAVING clauses ofSELECT statements, in theWHERE clause of aSELECT,DELETE, orUPDATE statement, or inSET statements. Expressions can be written using values from several sources, such as literal values, column values,NULL, variables, built-in functions and operators, loadable functions, and stored functions (a type of stored object).

This chapter describes the built-in functions and operators that are permitted for writing expressions in MySQL. For information about loadable functions and stored functions, seeSection 5.6, “MySQL Server Loadable Functions”, andSection 23.2, “Using Stored Routines”. For the rules describing how the server interprets references to different kinds of functions, seeSection 9.2.5, “Function Name Parsing and Resolution”.

An expression that containsNULL always produces aNULL value unless otherwise indicated in the documentation for a particular function or operator.

For the sake of brevity, some examples in this chapter display the output from themysql 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