Chapter 12 Functions and Operators

Table of Contents

12.1 Function and Operator Reference
12.2 Type Conversion in Expression Evaluation
12.3 Operators
12.3.1 Operator Precedence
12.3.2 Comparison Functions and Operators
12.3.3 Logical Operators
12.3.4 Assignment Operators
12.4 Control Flow Functions
12.5 String Functions
12.5.1 String Comparison Functions
12.5.2 Regular Expressions
12.6 Numeric Functions and Operators
12.6.1 Arithmetic Operators
12.6.2 Mathematical Functions
12.7 Date and Time Functions
12.8 What Calendar Is Used By MySQL?
12.9 Full-Text Search Functions
12.9.1 Natural Language Full-Text Searches
12.9.2 Boolean Full-Text Searches
12.9.3 Full-Text Searches with Query Expansion
12.9.4 Full-Text Stopwords
12.9.5 Full-Text Restrictions
12.9.6 Fine-Tuning MySQL Full-Text Search
12.9.7 Adding a Collation for Full-Text Indexing
12.10 Cast Functions and Operators
12.11 XML Functions
12.12 Bit Functions
12.13 Encryption and Compression Functions
12.14 Information Functions
12.15 Spatial Analysis Functions
12.15.1 Spatial Function Reference
12.15.2 Argument Handling by Spatial Functions
12.15.3 Functions That Create Geometry Values from WKT Values
12.15.4 Functions That Create Geometry Values from WKB Values
12.15.5 MySQL-Specific Functions That Create Geometry Values
12.15.6 Geometry Format Conversion Functions
12.15.7 Geometry Property Functions
12.15.8 Spatial Operator Functions
12.15.9 Functions That Test Spatial Relations Between Geometry Objects
12.16 Miscellaneous Functions
12.17 Functions and Modifiers for Use with GROUP BY Clauses
12.17.1 GROUP BY (Aggregate) Functions
12.17.2 GROUP BY Modifiers
12.17.3 MySQL Handling of GROUP BY
12.18 Precision Math
12.18.1 Types of Numeric Values
12.18.2 DECIMAL Data Type Characteristics
12.18.3 Expression Handling
12.18.4 Rounding Behavior
12.18.5 Precision Math Examples

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 permitted for writing expressions in MySQL. Instructions for writing stored functions and user-defined functions are given in Section 19.2, “Using Stored Routines (Procedures and Functions)”, and Section 22.3, “Adding New Functions to MySQL”. See Section 9.2.4, “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 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 5.1.7, “Server SQL Modes”.) 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