Pattern matching is a versatile way of identifying character data. In SQL, the LIKE keyword is used to search for patterns. Pattern matching employs wildcard characters to match different combinations of characters.
The LIKE keyword indicates that the following character string is a matching pattern. LIKE is used with character data.
The syntax for LIKE is:
expression [ NOT ] LIKE match-expression
The expression to be matched is compared to a match-expression that can include these special symbols:
|%||Matches any string of 0 or more characters|
|_||Matches any one character|
The specifier in the brackets may take the following forms:
Note that the range [a-f], and the sets [abcdef] and [fcbdae] return the same set of values.
|[^specifier]||The caret symbol (^) preceding a specifier indicates non-inclusion. [^a-f] means not in the range a-f; [^a2bR] means not a, 2, b, or R.|
You can match the column data to constants, variables, or other columns that contain the wildcard characters displayed in the table. When using constants, you should enclose the match strings and character strings in single quotes.
All the following examples use LIKE with the Surname column in the Contacts table. Queries are of the form:
SELECT Surname FROM Contacts WHERE Surname LIKE match-expression;
The first example would be entered as
SELECT Surname FROM Contacts WHERE Surname LIKE 'Mc%';
|'Mc%'||Search for every name that begins with the letters Mc||McEvoy|
|'%er'||Search for every name that ends with er||Brier, Miller, Weaver, Rayner|
|'%en%'||Search for every name containing the letters en.||Pettengill, Lencki, Cohen|
|'_ish'||Search for every four-letter name ending in ish.||Fish|
|'Br[iy][ae]r'||Search for Brier, Bryer, Briar, or Bryar.||Brier|
|'[M-Z]owell'||Search for all names ending with owell that begin with a single letter in the range M to Z.||Powell|
|'M[^c]%'||Search for all names beginning with M' that do not have c as the second letter||Moore, Mulley, Miller, Masalsky|
Wildcard characters used without LIKE are interpreted as string literals rather than as a pattern: they represent exactly their own values. The following query attempts to find any phone numbers that consist of the four characters 415% only. It does not find phone numbers that start with 415.
SELECT Phone FROM Contacts WHERE Phone = '415%';
See also String literals.
You can use LIKE on date and time fields and on character data. When you use LIKE with date and time values, the dates are converted to the standard DATETIME format, and then to VARCHAR.
One feature of using LIKE when searching for DATETIME values is that, since date and time entries may contain a variety of date parts, an equality test has to be written carefully to succeed.
For example, if you insert the value 9:20 and the current date into a column named arrival_time, the following clause fails to find the value, because the entry holds the date and the time:
WHERE arrival_time = '9:20'
However, the clause below would find the 9:20 value:
WHERE arrival_time LIKE '%09:20%'
With NOT LIKE, you can use the same wildcard characters that you can use with LIKE. To find all the phone numbers in the Contacts table that do not have 415 as the area code, you can use either of these queries:
SELECT Phone FROM Contacts WHERE Phone NOT LIKE '415%';
SELECT Phone FROM Contacts WHERE NOT Phone LIKE '415%';
Another special character that can be used with LIKE is the _ (underscore) character, which matches exactly one character. For example, the pattern 'BR_U%' matches all names starting with BR and having U as the fourth letter. In Braun the _ character matches the letter A and the % matches N. See LIKE search condition.
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