MySQL

REGEXP Matching Multiple Instances

If you want to locate all numbers regardless of how many digits the number contains, or you might want to locate a word but also be able to accommodate a trailing s if one exists, and so on.

This can be accomplished using the regular expressions repetition metacharacters, listed in following table.

Metacharacter Description

*

0 or more matches

+

1 or more matches (equivalent to {1,})

?

0 or 1 match (equivalent to {0,1})

{n}

Specific number of matches

{n,}

No less than a specified number of matches

{n,m}

Range of matches (m not to exceed 255)


Following are some examples.

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

The above statement displayed the following output:

+------------------+
| prod_name        |
+------------------+
| abc (product 1)  |
| abc (product 2)  |
| abc (products 1) |
    .
    .
    .
| abc (products 10)|
+------------------+

Regular expression \\(products? [0-9]\\) requires some explanation. \\( matches (, [0-9] matches any digit, products? matches product and products (the ? after the s makes that s optional because ? matches 0 or 1 occurrence of whatever it follows), and \\) matches the closing ). Without ? it would have been very difficult to match both stick and sticks.

Here's another example. This time we'll try to match four consecutive digits:

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

The above code displayed the following output:

+--------------+
| prod_name    |
+--------------+
| product 1000 |
| product 2000 |
+--------------+

As explained previously, [:digit:] matches any digit, and so [[:digit:]] is a set of digits. {4} requires exactly four occurrences of whatever it follows (any digit), and so [[:digit:]]{4} matches any four consecutive digits.

It is worth noting that when using regular expressions there is almost always more than one way to write a specific expression. The previous example could have also been written as follows:

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

by BrainBellupdated
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