SQL wildcards are used within a table to search for data.  Usage of wildcard characters in SQL call for SQL LIKE operator, which enables to hold a comparison between a value and similar values.

Following are the two types of wildcard operators :

The percent sign (%) : Matches one or more characters. 

Syntax: 

SELECT FROM table_name
WHERE column LIKE 'XXXX%'

or 

SELECT FROM table_name
WHERE column LIKE '%XXXX%'

E.g: 

1.  

WHERE SALARY LIKE '500%'

Finds any values that start with 500

2.

WHERE SALARY LIKE '%600%'

Finds any values that have 600 in any position.

3.

WHERE SALARY LIKE '%5'

Finds any values that end with 5.

The underscore (_) : Matches one character.

Syntax: 

SELECT FROM table_name
WHERE column LIKE 'XXXX_'

or

SELECT FROM table_name
WHERE column LIKE '_XXXX'

or

SELECT FROM table_name
WHERE column LIKE '_XXXX_'

E.g.

1.

WHERE SALARY LIKE '4___8'

Finds any values in a five-digit number that start with 4 and end with 8.

2.

WHERE SALARY LIKE '_00%'

Finds any values that have 00 in the second and third positions.