The REGEXP_INSTR function in MySQL is used to search for a regular expression pattern in a string and return the position of the first occurrence of the pattern. It is particularly useful when you want to find the starting position of a substring that matches a specified regular expression within a larger string.

Syntax

Here is the syntax for the REGEXP_INSTR function:

REGEXP_INSTR(str, pattern [, start [, position [, occurrence [, match_type]]]])

str: The string to be searched.
pattern: The regular expression pattern to search for.
start (optional): The position in the string where the search should begin. The default is 1.
position (optional): The position in the string from where the search starts. The default is 1.
occurrence (optional): Specifies which occurrence of the pattern to search for. The default is 1.
match_type (optional): Specifies the type of match. It can be 0 (default) for simple match, 1 for case-insensitive match, and 2 for case-sensitive match.

Examples

Here are some examples of how to use the REGEXP_INSTR function:

1. Find the position of the first occurrence of the substring “abc” within the string “xyzabcefg”:

SELECT REGEXP_INSTR('xyzabcefg', 'abc');

This will return 4, which is the index of the fourth character in the string.

2. Find the position of the second occurrence of the substring “ab” within the string “aabbccc”:

SELECT REGEXP_INSTR('aabbccc', 'ab', 2);

This will return 6, which is the index of the sixth character in the string.

3. Find the position of the first occurrence of the pattern “^a.” within the string “hello”:

SELECT REGEXP_INSTR('hello', "^a.", 1, 1, 0);

This will return 1, which is the index of the first character of the match.

4. Find the position of the first occurrence of the pattern “[0-9]{3}” within the string “my phone number is 123-456-7890”:

SELECT REGEXP_INSTR('my phone number is 123-456-7890', '[0-9]{3}', 1, 1, 0);

This will return 16, which is the index of the first character of the match.

It’s important to note that the position is 1-based, meaning the first character in the string is at position 1. If the pattern is not found, the function returns 0.

Conclusion

Keep in mind that the actual use of regular expressions can be more complex, and you can tailor the pattern according to your specific requirements. The REGEXP_INSTR function is a powerful tool for searching patterns within strings based on regular expressions in MySQL.