9.1.1 String Literals

A string is a sequence of bytes or characters, enclosed within either single quote (') or double quote (") characters. Examples:

'a string'
"another string"

Quoted strings placed next to each other are concatenated to a single string. The following lines are equivalent:

'a string'
'a' ' ' 'string'

If the ANSI_QUOTES SQL mode is enabled, string literals can be quoted only within single quotation marks because a string quoted within double quotation marks is interpreted as an identifier.

A binary string is a string of bytes that has no character set or collation. A nonbinary string is a string of characters that has a character set and collation. For both types of strings, comparisons are based on the numeric values of the string unit. For binary strings, the unit is the byte. For nonbinary strings the unit is the character and some character sets support multibyte characters. Character value ordering is a function of the string collation.

String literals may have an optional character set introducer and COLLATE clause:

[_charset_name]'string' [COLLATE collation_name]

Examples:

SELECT _latin1'string';
SELECT _latin1'string' COLLATE latin1_danish_ci;

You can use N'literal' (or n'literal') to create a string in the national character set. These statements are equivalent:

SELECT N'some text';
SELECT n'some text';
SELECT _utf8'some text';

For more information about these forms of string syntax, see Section 10.1.3.5, “Character String Literal Character Set and Collation”, and Section 10.1.3.6, “National Character Set”.

Within a string, certain sequences have special meaning unless the NO_BACKSLASH_ESCAPES SQL mode is enabled. Each of these sequences begins with a backslash (\), known as the escape character. MySQL recognizes the escape sequences shown in Table 9.1, “Special Character Escape Sequences”. For all other escape sequences, backslash is ignored. That is, the escaped character is interpreted as if it was not escaped. For example, \x is just x. These sequences are case sensitive. For example, \b is interpreted as a backspace, but \B is interpreted as B. Escape processing is done according to the character set indicated by the character_set_connection system variable. This is true even for strings that are preceded by an introducer that indicates a different character set, as discussed in Section 10.1.3.5, “Character String Literal Character Set and Collation”.

Table 9.1 Special Character Escape Sequences

Escape SequenceCharacter Represented by Sequence
\0 An ASCII NUL (0x00) character.
\' A single quote (') character.
\" A double quote (") character.
\b A backspace character.
\n A newline (linefeed) character.
\r A carriage return character.
\t A tab character.
\Z ASCII 26 (Control+Z). See note following the table.
\\ A backslash (\) character.
\% A % character. See note following the table.
\_ A _ character. See note following the table.

The ASCII 26 character can be encoded as \Z to enable you to work around the problem that ASCII 26 stands for END-OF-FILE on Windows. ASCII 26 within a file causes problems if you try to use mysql db_name < file_name.

The \% and \_ sequences are used to search for literal instances of % and _ in pattern-matching contexts where they would otherwise be interpreted as wildcard characters. See the description of the LIKE operator in Section 12.5.1, “String Comparison Functions”. If you use \% or \_ outside of pattern-matching contexts, they evaluate to the strings \% and \_, not to % and _.

There are several ways to include quote characters within a string:

The following SELECT statements demonstrate how quoting and escaping work:

mysql> SELECT 'hello', '"hello"', '""hello""', 'hel''lo', '\'hello';
+-------+---------+-----------+--------+--------+
| hello | "hello" | ""hello"" | hel'lo | 'hello |
+-------+---------+-----------+--------+--------+

mysql> SELECT "hello", "'hello'", "''hello''", "hel""lo", "\"hello";
+-------+---------+-----------+--------+--------+
| hello | 'hello' | ''hello'' | hel"lo | "hello |
+-------+---------+-----------+--------+--------+

mysql> SELECT 'This\nIs\nFour\nLines';
+--------------------+
| This
Is
Four
Lines |
+--------------------+

mysql> SELECT 'disappearing\ backslash';
+------------------------+
| disappearing backslash |
+------------------------+

If you want to insert binary data into a string column (such as a BLOB column), you should represent certain characters by escape sequences. Backslash (\) and the quote character used to quote the string must be escaped. In certain client environments, it may also be necessary to escape NUL or Control+Z. The mysql client truncates quoted strings containing NUL characters if they are not escaped, and Control+Z may be taken for END-OF-FILE on Windows if not escaped. For the escape sequences that represent each of these characters, see Table 9.1, “Special Character Escape Sequences”.

When writing application programs, any string that might contain any of these special characters must be properly escaped before the string is used as a data value in an SQL statement that is sent to the MySQL server. You can do this in two ways: