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11.4.1. String Comparison Functions

Table 11.7. String Comparison Operators

Name Description
LIKE Simple pattern matching
NOT LIKE Negation of simple pattern matching
STRCMP() Compare two strings

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.

  • expr LIKE pat [ESCAPE 'escape_char']

    Pattern matching using SQL simple regular expression comparison. 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.

    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 significant, which is not true for CHAR or VARCHAR comparisons performed with the = operator: 

    mysql> SELECT 'a' = 'a ', 'a' LIKE 'a ';
+------------+---------------+
| 'a' = 'a ' | 'a' LIKE 'a ' |
+------------+---------------+
|          1 |             0 |
+------------+---------------+
1 row in set (0.00 sec)

    With LIKE you can use the following two wildcard characters in the pattern.

    Character Description
    % 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.

    String Description
    \% 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 following two statements illustrate that string comparisons are not case sensitive unless one of the operands is a binary string: 

    mysql> SELECT 'abc' LIKE 'ABC';
        -> 1
mysql> SELECT 'abc' LIKE BINARY 'ABC';
        -> 0

    In MySQL, LIKE is allowed on numeric expressions. (This is an extension to the standard SQL LIKE.) 

    mysql> SELECT 10 LIKE '1%';
        -> 1

    Note

    Because MySQL uses C escape syntax in strings (for example, “\n” to represent a newline character), you must double any “\” that you use in LIKE strings. 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']).

    Note

    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 expr always returns NULL, 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(expr1,expr2)

    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 1 otherwise. 

    mysql> SELECT STRCMP('text', 'text2');
        -> -1
mysql> SELECT STRCMP('text2', 'text');
        -> 1
mysql> SELECT STRCMP('text', 'text');
        -> 0

    As of MySQL 4.0, STRCMP() uses the current character set when performing comparisons. This makes the default comparison behavior case insensitive unless one or both of the operands are binary strings. Before MySQL 4.0, STRCMP() is case sensitive.


User Comments

Posted by Sascha René Leib on October 10 2002 1:29am[Delete] [Edit]

Also, keep in mind that by default,
Swedish/Finnish string comparison rules are in
use! This means that e.g.: u <> ü = y !

Posted by Jeremy Schultz on May 4 2004 8:10pm[Delete] [Edit]

In the manual it states "Before MySQL 4.0, STRCMP() is case sensitive.", I did not relize this, and I found out the hard way that STRCMP() is case-sensitive.

Also I found it strange that STRCMP() is case-sensitive, but ORDER BY is case-insensitive.

Here is the what I was doing, and I hope this helps others. I have a table that I display, just a basic dump of the table order by a varchar field. I have a section to display a single item from the list, then used the STRCMP to go to the next/prevoius item in the order it was displayed

Listing the table:
SELECT id, name, price, description WHERE category = 1 ORDER BY name

Getting the Next Item Button for display section:
SELECT id WHERE category = 1 AND STRCMP(name, 'current_item_name') = 1 ORDER BY name LIMIT 1

Getting the Prev Item Button for display section:
SELECT id WHERE category = 1 AND STRCMP(name, 'current_item_name') = -1 ORDER BY name DESC LIMIT 1

The Fix I use for now, is to lowercase the strings in STRCMP():
STRCMP(LOWER(name), LOWER('current_item_name'))

Posted by Ami Chayun on January 12 2006 9:16am[Delete] [Edit]

It is possible to search wildchar patterns when using bind parameters.
For example to search a substring:

select * from tblUser where Name LIKE CONCAT('%', ? ,'%');

And then (for example in perl DBI)
$dbh->selectrow_hashref($SQL_Stmnt, undef, @{[ 'Erik']});

This provides a 'safer' search environment in web interfaces, since it prevents SQL injections.

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