如何使用SQL确定两个不同表中邮政编码的前几个字符？

Question

So I've run into a bit of an issue. I can't seem to get my head around this problem and was wondering if I could get a bit of help.

I've got two tables both containing postcode related information.

Table A contains the full postcode, Table B contains the prefix for the area.

So for example table A contains the postcode NE628HJ and table b contains NE62. How do I query it to select all the similar ones?

I've tried this:

SELECT * from tableB
left join tableA
       on tableA.postcode LIKE tableB.postcode

but this doesn't work.

Any suggestions?

Answer 1

You can use wildcards in the like :

SELECT *
from tableB left join
     tableA
     on tableA.postcode LIKE tableB.postcode + '%';

Performance will not be particularly good, because this will not take advantage of indexes.

Answer 2

You can use

SELECT * from tableB
left join tableA
       on left(tableA.postcode,2) = left(tableB.postcode,2)

to match on the 2 char prefix