[MySQL must know and know (6)] [Search with regular expressions]

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1. Introduction to regular expressions

All kinds of programming languages, text editors, and operating systems support regular expressions.

Second, use MySQL regular expressions

MySQL provides preliminary support for regular expressions with the WHERE clause, allowing you to specify regular expressions and filter the data retrieved by SELECT

Only a subset of the regular expression language
MySQL supports only a small subset of most regular expression implementations

2.1 Basic character matching

mysql> SELECT prod_name
    -> FROM products
    -> WHERE prod_name REGEXP '1000'
    -> ORDER BY prod_name;

analysis

This statement looks very much like a statement using LIKE. What follows REGEXP is treated as a regular expression

mysql> SELECT prod_name
    -> FROM products
    -> WHERE prod_name REGEXP '.000'
    -> ORDER BY prod_name;

analysis

. Is a special character in regular expression language. It means to match any character, so 1000 and 2000 are matched and return

LIKE与REGEXP

LIKE matches the entire column. If the matched text appears in the column value, LIKE will not be found, and the corresponding row will not be returned. While REGEXP matches within the column value, if the matched text appears in the column value, REGEXP will find it and the corresponding row will be returned.

2.2 Perform OR matching

To search for one of two strings, use |

mysql> SELECT prod_name
    -> FROM products
    -> WHERE prod_name REGEXP '1000|2000'
    -> ORDER BY prod_name;

2.3 Match one of several characters

By specifying a set of characters enclosed in [and]

mysql> SELECT prod_name
    -> FROM products
    -> WHERE prod_name REGEXP '[123] Ton'
    -> ORDER BY prod_name;

analysis

[123]Ton is the abbreviation of [1|2|3]Ton

mysql> SELECT prod_name
    -> FROM products
    -> WHERE prod_name REGEXP '1|2|3 Ton'
    -> ORDER BY prod_name;

analysis

[^123] matches anything except these characters

2.4 Matching range

Sets can be used to define one or more characters to match

The range is not limited to the complete set, the range is not necessarily just a number, [az] matches any character

mysql> SELECT prod_name
    -> FROM products
    -> WHERE prod_name REGEXP '[1-5] Ton'
    -> ORDER BY prod_name;

2.5 match special characters

mysql> SELECT vend_name
    -> FROM vendors
    -> WHERE vend_name REGEXP '.'
    -> ORDER BY vend_name;

analysis

. Matches any character, so every line is retrieved

mysql> SELECT vend_name
    -> FROM vendors
    -> WHERE vend_name REGEXP '\\.'
    -> ORDER BY vend_name;

match\

In order to match the backslash character itself, you need to use \\

2.6 Matching multiple instances

mysql> SELECT prod_name
    -> FROM products
    -> WHERE prod_name REGEXP '\\([0-9] sticks?\\)'
    -> ORDER BY prod_name;

analysis

[0-9] Match any number
sticks? Match sticks and sticks

mysql> SELECT prod_name
    -> FROM products
    -> WHERE prod_name REGEXP '[[:digit:]]{4}'
    -> ORDER BY prod_name;

analysis

[:digit:] matches any digit
{4} requires the character before it to appear 4 times

mysql> SELECT prod_name
    -> FROM products
    -> WHERE prod_name REGEXP '[0-9][0-9][0-9][0-9]'
    -> ORDER BY prod_name;

2.8 Locator

mysql> SELECT prod_name
    -> FROM products
    -> WHERE prod_name REGEXP '^[0-9\\.]'
    -> ORDER BY prod_name;

analysis

^The beginning of the match string

Make REGXP behave like LIKE

The difference between LIKE and REGEXP is that LIKE matches the entire string and REGEXP matches the string. Using locators, by starting each expression with ^ and ending each expression with $, you can make REGEXP the same as LIKE

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