Regular Expressions

Introduction#

A regular expression is a powerful way of specifying a pattern for a complex search.

REGEXP / RLIKE

The REGEXP (or its synonym, RLIKE) operator allows pattern matching based on regular expressions.

Consider the following employee table:

+-------------+-------------+-------------+--------------+----------+
| EMPLOYEE_ID | FIRST_NAME  | LAST_NAME   | PHONE_NUMBER | SALARY   |
+-------------+-------------+-------------+--------------+----------+
|         100 | Steven      | King        | 515.123.4567 | 24000.00 |
|         101 | Neena       | Kochhar     | 515.123.4568 | 17000.00 |
|         102 | Lex         | De Haan     | 515.123.4569 | 17000.00 |
|         103 | Alexander   | Hunold      | 590.423.4567 |  9000.00 |
|         104 | Bruce       | Ernst       | 590.423.4568 |  6000.00 |
|         105 | David       | Austin      | 590.423.4569 |  4800.00 |
|         106 | Valli       | Pataballa   | 590.423.4560 |  4800.00 |
|         107 | Diana       | Lorentz     | 590.423.5567 |  4200.00 |
|         108 | Nancy       | Greenberg   | 515.124.4569 | 12000.00 |
|         109 | Daniel      | Faviet      | 515.124.4169 |  9000.00 |
|         110 | John        | Chen        | 515.124.4269 |  8200.00 |
+-------------+-------------+-------------+--------------+----------+

Pattern ^

Select all employees whose FIRST_NAME starts with N.

Query

SELECT * FROM employees WHERE FIRST_NAME REGEXP '^N'
-- Pattern start with----------------------------^

Pattern $**

Select all employees whose PHONE_NUMBER ends with 4569.

Query

SELECT * FROM employees WHERE PHONE_NUMBER REGEXP '4569$'
-- Pattern end with----------------------------------^

NOT REGEXP

Select all employees whose FIRST_NAME does not start with N.

Query

SELECT * FROM employees WHERE FIRST_NAME NOT REGEXP '^N'
-- Pattern does not start with---------------^

Regex Contain

Select all employees whose LAST_NAME contains in and whose FIRST_NAME contains a.

Query

SELECT * FROM employees WHERE FIRST_NAME REGEXP 'a' AND LAST_NAME REGEXP 'in'
-- No ^ or $, pattern can be anywhere -------------------------------------^

Any character between [ ]

Select all employees whose FIRST_NAME starts with A or B or C.

Query

SELECT * FROM employees WHERE FIRST_NAME REGEXP '^[ABC]'
-------------------------------------------------^^---^

Pattern or |

Select all employees whose FIRST_NAME starts with A or B or C and ends with r, e, or i.

Query

SELECT * FROM employees WHERE FIRST_NAME REGEXP '^[ABC]|[rei]$'
-- ----------------------------------------------^^---^^^---^^

Counting regular expression matches

Consider the following query:

SELECT FIRST_NAME, FIRST_NAME REGEXP '^N' as matching FROM employees

FIRST_NAME REGEXP '^N' is 1 or 0 depending on the fact that FIRST_NAME matches ^N.

To visualize it better:

SELECT 
FIRST_NAME, 
IF(FIRST_NAME REGEXP '^N', 'matches ^N', 'does not match ^N') as matching 
FROM employees

Finally, count total number of matching and non-matching rows with:

SELECT
IF(FIRST_NAME REGEXP '^N', 'matches ^N', 'does not match ^N') as matching,
COUNT(*) 
FROM employees 
GROUP BY matching