What does the percent sign mean in mysql?

In MySQL, the percent sign (%) is used as a wildcard character to match zero or more characters in a string. It can be used in wildcard strings, LIKE clauses and REGEXP functions, such as matching with "John" is the name of the substring (the row starting with "Jo" in "my_table").

The percent sign (%) in MySQL

The role of the percent sign:

The percent sign (%) is used to represent wildcard characters in MySQL. It matches zero or more characters.

Detailed explanation:

Percent signs can appear in the following positions:

• Wildcard characters in strings :

  • Use % in a string to match zero or more characters. For example, "my_table%" will match all table names starting with "my_table".

• Wildcard characters in the LIKE clause:

  • In the LIKE clause, % can be used as a wildcard character to match Zero or more characters. For example, "SELECT * FROM my_table WHERE name LIKE "%John%" will match all rows whose names contain the string "John".

• Wildcards in the REGEXP function:

  ##The REGEXP function uses % as a greedy quantifier to match zero or more previous characters. For example,
  • "SELECT * FROM my_table WHERE. name REGEXP "J.*n" will match all names starting with "J" and ending with "n".

Example:

SELECT * FROM my_table WHERE name LIKE "Jo%"; -- 匹配名称以 "Jo" 开头的行
SELECT * FROM my_table WHERE name REGEXP "^[A-Z].*%"; -- 匹配名称以大写字母开头且包含一个或多个字母的行

Note:

Percent sign is a special character in MySQL, so when using it as a wildcard character, it must be escaped with a backslash (). For example, to match the actual percent sign character, use
• "%%".
In some cases, using wildcards may reduce query performance. Therefore, it is recommended to use them with caution when necessary.

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