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SQL Anywhere 11.0.1 (Français) » SQL Anywhere Server - SQL Usage » Querying and Modifying Data » Querying data » The WHERE clause: Specifying rows

 

Matching character strings in the WHERE clause

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:

Symbols Meaning
% Matches any string of 0 or more characters
_ Matches any one character
[specifier]

The specifier in the brackets may take the following forms:

  • Range   A range is of the form rangespec1-rangespec2, where rangespec1 indicates the start of a range of characters, the hyphen indicates a range, and rangespec2 indicates the end of a range of characters

  • Set   A set can include any discrete set of values, in any order. For example, [a2bR].

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.

Examples

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%';
Match expression Description Returns
'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
Wildcards require LIKE

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.

Using LIKE with date and time values

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%'
Using NOT LIKE

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%';
Using underscores

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.