Harish Shetty Harish Shetty - 17 days ago 11
SQL Question

What is the equivalent of REGEXP_SUBSTR in mysql?

I want to extract a word from a string column of a table.

description
===========================
abc order_id: 2 xxxx yyy aa
mmm order_id: 3 nn kk yw


Expected result set

order_id
===========================
2
3


Table will at most have 100 rows, text length is ~256 char and column always has one
order_id
present. So performance is not an issue.

In Oracle, I can use
REGEXP_SUBSTR
for this problem. How would I solve this in MySQL?

Edit 1

I am using LOCATE and SUBSTR to solve the problem. The code is ugly. Ten minutes after writing the code, I am cursing the guy who wrote such an ugly code.

I didn't find the REGEXP_SUBSTR function in MySQL docs. But I am hoping that it exists..

Answer to : Why cant the table be optimized? Why is the data stored in such a dumb fashion?

The example I gave just denotes the problem I am trying to solve. In real scenario, I am using a DB based 3rd party queuing software for executing asynchronous tasks. The queue serializes the Ruby object as text. I have no control over the table structure OR the data format. The tasks in the queue can be recurring. In our test setup, some of the recurring tasks are failing because of stale data. I have to delete these tasks to prevent the error. Such errors are not common, hence I don't want to maintain a normalized shadow table.

Answer

Like Konerak said, there is no equivalent of REGEXP_SUBSTR in MySql. You could do what you need using SUBSTRING logic, but it is ugly :

SELECT
  SUBSTRING(lastPart.end, 1, LOCATE(' ', lastPart.end) - 1) AS orderId
FROM
  (
    SELECT
      SUBSTRING(dataset.description, LOCATE('order_id: ', dataset.description) + LENGTH('order_id: ')) AS end
    FROM
      (
        SELECT 'abc order_id: 2 xxxx yyy aa' AS description
        UNION SELECT 'mmm order_id: 3 nn kk yw' AS description
        UNION SELECT 'mmm order_id: 1523 nn kk yw' AS description
      ) AS dataset
    ) AS lastPart

Edit: You could try this user defined function providing access to perl regex in MySql

SELECT 
  PREG_CAPTURE( '/.*order_id:\s(\d+).*/', dataset.description,1)
FROM
  (
    SELECT 'abc order_id: 2 xxxx yyy aa' AS description
    UNION SELECT 'mmm order_id: 3 nn kk yw' AS description
    UNION SELECT 'mmm order_id: 1523 nn kk yw' AS description
  ) AS dataset