What does sql wildcard mean?

SQL wildcards allow you to use special characters (%), (_), ([]) and ([^]) to match a wide range of values ​​in a SELECT statement, thus writing more general queries. They are used to match any character, a single character, a sequence of characters within square brackets, and a sequence of characters outside square brackets, respectively. Use wildcards with caution, as different DBMSs have different regulations, abuse can lead to query performance problems.

SQL wildcards

SQL wildcards are special characters that allow you to match a series of values ​​in a WHERE clause. By using wildcards, you can write more flexible and general queries.

Commonly used SQL wildcards

• % : Match any number of characters.

  • For example: SELECT * FROM table WHERE name LIKE '%John%'; will match all names containing the "John" string.

• _ : Match a single character.

  • For example: SELECT * FROM table WHERE name LIKE '_ohn'; will match all names starting with "John".

• [] : Match the sequence of characters specified in brackets.

  • For example: SELECT * FROM table WHERE name LIKE '[Jj][Oo][Hh][Nn]'; will match all names ending with "John" or "john".

• [^] : Matches the sequence of characters not specified in square brackets.

  • For example: SELECT * FROM table WHERE name LIKE '[^a]ohn'; will match all names that do not start with "a" end with "John".

Example of using wildcard characters

Here are some examples of SQL queries using wildcards:

• Find all names starting with "A": SELECT * FROM table WHERE name LIKE 'A%';
• Find all names containing "er" strings: SELECT * FROM table WHERE name LIKE '%er%';
• Find all names happen to be "John": SELECT * FROM table WHERE name LIKE '_ohn';
• Find all names that do not start with "a": SELECT * FROM table WHERE name LIKE '[^a]%';

Notice:

• Wildcard usage varies by different database management systems (DBMS).
• Abuse of wildcards can lead to poor query performance.
• Be careful when using wildcards to avoid unexpected matches.

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