MySQL 8.0 Reference Manual Including MySQL NDB Cluster 8.0
If a string function is given a binary string as an argument, the resulting string is also a binary string. A number converted to a string is treated as a binary string. This affects only comparisons.
Normally, if any expression in a string comparison is case-sensitive, the comparison is performed in case-sensitive fashion.
If a string function is invoked from within the
mysql client, binary strings display using
hexadecimal notation, depending on the value of the
--binary-as-hex. For more
information about that option, see Section 6.5.1, “mysql — The MySQL Command-Line Client”.
expr
LIKE pat [ESCAPE
'escape_char']
Pattern matching using an SQL pattern. Returns
1 (TRUE) or
0 (FALSE). If either
expr or
pat is NULL,
the result is NULL.
The pattern need not be a literal string. For example, it can be specified as a string expression or table column. In the latter case, the column must be defined as one of the MySQL string types (see Section 13.3, “String Data Types”).
Per the SQL standard, LIKE
performs matching on a per-character basis, thus it can
produce results different from the
= comparison
operator:
mysql>SELECT 'ä' LIKE 'ae' COLLATE latin1_german2_ci;+-----------------------------------------+ | 'ä' LIKE 'ae' COLLATE latin1_german2_ci | +-----------------------------------------+ | 0 | +-----------------------------------------+ mysql>SELECT 'ä' = 'ae' COLLATE latin1_german2_ci;+--------------------------------------+ | 'ä' = 'ae' COLLATE latin1_german2_ci | +--------------------------------------+ | 1 | +--------------------------------------+
In particular, trailing spaces are always significant. This
differs from comparisons performed with the
= operator,
for which the significance of trailing spaces in nonbinary
strings (CHAR,
VARCHAR, and TEXT
values) depends on the pad attribute of the collation used
for the comparison. For more information, see
Trailing Space Handling in Comparisons.
With LIKE you can use the
following two wildcard characters in the pattern:
% matches any number of characters,
even zero characters.
_ matches exactly one character.
mysql>SELECT 'David!' LIKE 'David_';-> 1 mysql>SELECT 'David!' LIKE '%D%v%';-> 1
To test for literal instances of a wildcard character,
precede it by the escape character. If you do not specify
the ESCAPE character,
\ is assumed, unless the
NO_BACKSLASH_ESCAPES SQL
mode is enabled. In that case, no escape character is used.
\% matches one %
character.
\_ matches one _
character.
mysql>SELECT 'David!' LIKE 'David\_';-> 0 mysql>SELECT 'David_' LIKE 'David\_';-> 1
To specify a different escape character, use the
ESCAPE clause:
mysql> SELECT 'David_' LIKE 'David|_' ESCAPE '|';
-> 1
The escape sequence should be one character long to specify
the escape character, or empty to specify that no escape
character is used. The expression must evaluate as a
constant at execution time. If the
NO_BACKSLASH_ESCAPES SQL
mode is enabled, the sequence cannot be empty.
The following statements illustrate that string comparisons are not case-sensitive unless one of the operands is case-sensitive (uses a case-sensitive collation or is a binary string):
mysql>SELECT 'abc' LIKE 'ABC';-> 1 mysql>SELECT 'abc' LIKE _utf8mb4 'ABC' COLLATE utf8mb4_0900_as_cs;-> 0 mysql>SELECT 'abc' LIKE _utf8mb4 'ABC' COLLATE utf8mb4_bin;-> 0 mysql>SELECT 'abc' LIKE BINARY 'ABC';-> 0
As an extension to standard SQL, MySQL permits
LIKE on numeric expressions.
mysql> SELECT 10 LIKE '1%';
-> 1
MySQL attempts in such cases to perform implicit conversion of the expression to a string. See Section 14.3, “Type Conversion in Expression Evaluation”.
MySQL uses C escape syntax in strings (for example,
\n to represent the newline character).
If you want a LIKE string to
contain a literal \, you must double
it. (Unless the
NO_BACKSLASH_ESCAPES SQL
mode is enabled, in which case no escape character is
used.) For example, to search for \n,
specify it as \\n. To search for
\, specify it as
\\\\; this is because the backslashes
are stripped once by the parser and again when the pattern
match is made, leaving a single backslash to be matched
against.
Exception: At the end of the pattern string, backslash can
be specified as \\. At the end of the
string, backslash stands for itself because there is
nothing following to escape. Suppose that a table contains
the following values:
mysql> SELECT filename FROM t1;
+--------------+
| filename |
+--------------+
| C: |
| C:\ |
| C:\Programs |
| C:\Programs\ |
+--------------+
To test for values that end with backslash, you can match the values using either of the following patterns:
mysql>SELECT filename, filename LIKE '%\\' FROM t1;+--------------+---------------------+ | filename | filename LIKE '%\\' | +--------------+---------------------+ | C: | 0 | | C:\ | 1 | | C:\Programs | 0 | | C:\Programs\ | 1 | +--------------+---------------------+ mysql>SELECT filename, filename LIKE '%\\\\' FROM t1;+--------------+-----------------------+ | filename | filename LIKE '%\\\\' | +--------------+-----------------------+ | C: | 0 | | C:\ | 1 | | C:\Programs | 0 | | C:\Programs\ | 1 | +--------------+-----------------------+
expr
NOT LIKE pat [ESCAPE
'escape_char']
This is the same as NOT
(.
expr LIKE
pat [ESCAPE
'escape_char'])
Aggregate queries involving NOT
LIKE comparisons with columns containing
NULL may yield unexpected results. For
example, consider the following table and data:
CREATE TABLE foo (bar VARCHAR(10)); INSERT INTO foo VALUES (NULL), (NULL);
The query SELECT COUNT(*) FROM foo WHERE bar LIKE
'%baz%'; returns 0. You might
assume that SELECT COUNT(*) FROM foo WHERE bar
NOT LIKE '%baz%'; would return
2. However, this is not the case: The
second query returns 0. This is because
NULL NOT LIKE
always returns
exprNULL, regardless of the value of
expr. The same is true for
aggregate queries involving NULL and
comparisons using
NOT
RLIKE or NOT
REGEXP. In such cases, you must test explicitly
for NOT NULL using
OR (and not
AND), as shown here:
SELECT COUNT(*) FROM foo WHERE bar NOT LIKE '%baz%' OR bar IS NULL;
STRCMP() returns
0 if the strings are the same,
-1 if the first argument is smaller than
the second according to the current sort order, and
NULL if either argument is
NULL. It returns 1
otherwise.
mysql>SELECT STRCMP('text', 'text2');-> -1 mysql>SELECT STRCMP('text2', 'text');-> 1 mysql>SELECT STRCMP('text', 'text');-> 0
STRCMP() performs the
comparison using the collation of the arguments.
mysql>SET @s1 = _utf8mb4 'x' COLLATE utf8mb4_0900_ai_ci;mysql>SET @s2 = _utf8mb4 'X' COLLATE utf8mb4_0900_ai_ci;mysql>SET @s3 = _utf8mb4 'x' COLLATE utf8mb4_0900_as_cs;mysql>SET @s4 = _utf8mb4 'X' COLLATE utf8mb4_0900_as_cs;mysql>SELECT STRCMP(@s1, @s2), STRCMP(@s3, @s4);+------------------+------------------+ | STRCMP(@s1, @s2) | STRCMP(@s3, @s4) | +------------------+------------------+ | 0 | -1 | +------------------+------------------+
If the collations are incompatible, one of the arguments must be converted to be compatible with the other. See Section 12.8.4, “Collation Coercibility in Expressions”.
mysql> SET @s1 = _utf8mb4 'x' COLLATE utf8mb4_0900_ai_ci; mysql> SET @s2 = _utf8mb4 'X' COLLATE utf8mb4_0900_ai_ci; mysql> SET @s3 = _utf8mb4 'x' COLLATE utf8mb4_0900_as_cs; mysql> SET @s4 = _utf8mb4 'X' COLLATE utf8mb4_0900_as_cs; --> mysql>SELECT STRCMP(@s1, @s3);ERROR 1267 (HY000): Illegal mix of collations (utf8mb4_0900_ai_ci,IMPLICIT) and (utf8mb4_0900_as_cs,IMPLICIT) for operation 'strcmp' mysql>SELECT STRCMP(@s1, @s3 COLLATE utf8mb4_0900_ai_ci);+---------------------------------------------+ | STRCMP(@s1, @s3 COLLATE utf8mb4_0900_ai_ci) | +---------------------------------------------+ | 0 | +---------------------------------------------+