Wildcards are used in SQL to match a string pattern. There are two types of wildcards:
% (percent sign) represents zero, one, or more characters.
_ (underscore) represents exactly one character.
Wildcards are used with the LIKE operator in SQL. The application of wildcard in SQL will be shown in the SQL LIKE section.
Examples
Below are some wildcard examples:
'A_Z': All string that starts with 'A', another character, and end with 'Z'. For example, 'ABZ' and 'A2Z' would both satisfy the condition, while 'AKKZ' would not (because there are two characters between A and Z instead of one).
'ABC%': All strings that start with 'ABC'. For example, 'ABCD' and 'ABCABC' would both satisfy the condition.
'%XYZ': All strings that end with 'XYZ'. For example, 'WXYZ' and 'ZZXYZ' would both satisfy the condition.
'%AN%': All strings that contain the pattern 'AN' anywhere. For example, 'LOS ANGELES' and 'SAN FRANCISCO' would both satisfy the condition.
'_AN%': All strings that contain a character, then 'AN', followed by anything else. For example, 'SAN FRANCISCO' would satisfy the condition, while 'LOS ANGELES' would not satisfy the condition.
Exercises
1. Which of the following strings satisfies the condition 'T_'? (There can be more than one answer)
a) TW
b) TWITTER
c) TAIWAN
d) To
2. Which of the following strings satisfies the condition 'A_B%'? (There can be more than one answer)
a) AKKB
b) AKBK
c) ABKK
d) ABBB
3. Which of the following strings satisfies the condition 'Z%K_R'? (There can be more than one answer)
a) ZKRR
b) ZJJR
c) ZRKKJ
d) ZABCDEFKR