wild card characters in sql

 Wildcard characters in SQL are special characters that allow you to perform pattern matching in string comparisons. These characters are often used in conjunction with the LIKE operator to filter rows based on specific patterns within text columns. The two main wildcard characters in SQL are the percent sign (%) and underscore (_).

1. Percent Sign (%) Wildcard:

   • The percent sign (%) represents zero or more characters in a string.
   • Syntax: SELECT column_name FROM table_name WHERE column_name LIKE 'pattern%';
   • Example:

     sql
     SELECT * FROM employees WHERE employee_name LIKE 'J%';
     

     This query retrieves all employees whose names start with the letter 'J'.

2. Underscore (_) Wildcard:

   • The underscore (_) represents a single character in a string.
   • Syntax: SELECT column_name FROM table_name WHERE column_name LIKE 'pattern_';
   • Example:

     sql
     SELECT * FROM products WHERE product_code LIKE 'AB_%';
     

     This query retrieves products with codes starting with 'AB' followed by any single character.

Combined Wildcards: You can also combine these wildcard characters to create more complex patterns:

• LIKE 'pattern%' matches strings that start with 'pattern'.
• LIKE '%pattern' matches strings that end with 'pattern'.
• LIKE '%pattern%' matches strings that contain 'pattern' anywhere in the string.

Note:

• The LIKE operator is case-insensitive by default in many SQL database systems, but this behavior can vary. You can use the COLLATE clause to specify case sensitivity if needed.
• Wildcard characters can affect query performance, especially when used at the beginning of a pattern, as they can prevent efficient index usage. It's essential to use wildcards judiciously to avoid performance issues.

Do you need more examples or information about using wildcard characters in SQL queries?