Question

I need to do the following and I’m struggling with the syntax:

I have a table called ‘mytable’ and a column called ‘mycolumn’ (string).

In mycolumn the value is a constructed value – for example, one of the values is: ‘first:10:second:18:third:31’. The values in mycolumn are all using the same pattern, just the ids/numbers are different.

I need to change the value of 18 (in this particular case) to a value from another tables key. The end result for this column value should be ‘first:10:second:22:third:31’ because I replaced 18 with 22. I got the 22 from another table using the 18 as a lookup value.

So ideally I would have the following:

UPDATE mytable 
SET mycolumn = [some regex function to find the number between 'second:' and ":third" - 
let's call that oldkey - and replace it with other id from another table - 
(select otherid from tableb where id = oldkey)].

I know the mysql has a REPLACE function but that doesn’t get me far enough.

Answer 1

You can create your own function. I am scared of REGEX so I use SUBSTRING and SUBSTRING_INDEX.

CREATE FUNCTION SPLIT_STRING(str VARCHAR(255), delim VARCHAR(12), pos INT)
RETURNS VARCHAR(255)
RETURN REPLACE(SUBSTRING(SUBSTRING_INDEX(str, delim, pos),
   LENGTH(SUBSTRING_INDEX(str, delim, pos-1)) + 1),
   delim, '');

SPLIT_STRING('first:10:second:18:third:31', ':', 4)

returns 18

Based on this answer:

Equivalent of explode() to work with strings in MySQL