Joining two strings using rlike

Question

I am joining the tables Table_A and Table_B on columns Col_A and Col_B . Below are some test sample values.

Table_A, Col_A
USA1FullCover
USAMainland
USA2Islands

Table_B, Col_B
USA
USA1
USA2

When joining, I need to match the value ' USA ' followed by a number exactly. For instance, the join result should look like this.

Col_A          Col_B
USA1FullCover  USA1
USAMainland    USA
USA2Island     USA2

I'm trying to achieve this in MySQL. I tried the rlike function. But the issue is that with rlike , I am not able to completely match them.

select
case when 'USA1FullCover' rlike 'USA' then 1 else 0 end;
#matches, but shouldn't

select
case when 'USA1FullCover' rlike 'USA1' then 1 else 0 end;
#matches, which is what I need/expect

select
case when 'USA1FullCover' rlike 'USA2' then 1 else 0 end;
#doesn't match, which is what I need/expect

My question is how can I fix the rlike so that the first case doesn't happen ie it doesn't match when there is no digit on the RHS? Or is it possible using regex ? Taking a substring of the LHS doesn't help since we cannot really define the length beforehand.

Answer 1

Use

col_A regexp '^USA[0-9]{1}.+$'

to match USA followed by exactly one digit followed by any other characters.

To join only when such pattern exists

select a.*,b.*
from tableA a
join tableB b on 
case when a.col_A regexp '^USA[0-9]{1}.+$' then substring(a.col_A,1,4) else '' end
= b.col_B