How to change rows in a table based on other table rows in mysql?

Posted by understack on Stack Overflow See other posts from Stack Overflow or by understack
Published on 2010-04-05T22:15:23Z Indexed on 2010/04/05 22:23 UTC
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php

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mysql

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row

I've a table which has 3 columns: id, a_id and b_id.

Suppose rows are like this:

1, a1, b1
2, a1, b2
3, a1, b3
4, a2, b4
5, a2, b5
6, a2, b6

I want to convert it to

1, a1, b1
2, a1, b1
3, a1, b1
4, a2, b4
5, a2, b4
6, a2, b4

So I want to make all the b_id corresponding to a_id same, and equal to the one which is found first. How can I do this? For simplicity, I've removed other columns from table. So please ignore row duplication here.

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