Question

Combing column values in JOIN statement

Asked by: alex_wareing

I'm trying to make a LEFT join using SQL. However the fields I am trying to join are not exactly the same. I have two tables  'geonams' and 'admin1codes' the key in 'admin1codes' is like this 'FR.01' and the 'geoname' table contains two columns that make up this key so there is a 'geoname.country' that is 'FR' and an 'admin1' that is '01'.

My question is how can i combine these two columns to test for a match in the other table, my attempt was:
LEFT JOIN admin1codes ON admin1codes.code = geoname.country + '.' + geoname.admin1

But that didn't work, how do i do this?

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Asked On
2009-08-12 at 12:13:08ID24647623
Topics

SQL Query Syntax

,

MySQL Server

Participating Experts
1
Points
500
Comments
7

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Answers

 

by: angelIIIPosted on 2009-08-12 at 12:18:21ID: 25081861

the code you showed is correct.
however, if any of the fields is CHAR instead of VARCHAR, this might explain things...

 

by: alex_wareingPosted on 2009-08-12 at 12:55:39ID: 25082230

Both feilds are VARCHAR but geoname.country + '.' + geoname.admin1 returns 0

 

by: angelIIIPosted on 2009-08-12 at 12:59:14ID: 25082267

ok, please try this:

LEFT JOIN admin1codes ON admin1codes.code = cast(geoname.country as varchar(30)) + '.' + cast(geoname.admin1 as varchar(30)) 

                                              
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by: alex_wareingPosted on 2009-08-12 at 13:02:50ID: 25082296

I get the error:

"You have an error in your SQL syntax; check the manula that corresponds to your MySQL server version for the right syntacx to use near 'varchar(30)) + '.' + cast(geoname.admin1 as varchar(30))' at line 3

Full SQL i'm using:

SELECT geoname.geonameid, geoname.name, geoname.country, geoname.admin1, admin1codes.code, admin1codes.name
FROM geoname
LEFT JOIN admin1codes ON admin1codes.code = cast(geoname.country as varchar(30)) + '.' + cast(geoname.admin1 as varchar(30))
WHERE geoname.geonameid = '2639912'
                                              
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by: angelIIIPosted on 2009-08-12 at 13:09:37ID: 25082368

AAAAAAAHHH MySQL ... not MSSQL ... my fault 

SELECT geoname.geonameid, geoname.name, geoname.country, geoname.admin1, admin1codes.code, admin1codes.name
FROM geoname
LEFT JOIN admin1codes ON admin1codes.code = CONCAT(geoname.country,'.',geoname.admin1)
WHERE geoname.geonameid = '2639912'

                                              
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by: alex_wareingPosted on 2009-08-12 at 13:20:20ID: 31614980

Thank-you, thank-you, THANK-YOU!

Has been driving me crazy all afternoon, i should of mentioned in the question it was MySQL. Thanks again.

 

by: angelIIIPosted on 2009-08-12 at 13:23:16ID: 25082512

>i should of mentioned in the question it was MySQL.
actually, you HAD. via the zone selection... I just had not put my glasses on..


now, to "explain" what happens in mysql when you use +: is makes the "maths", and not string concatenation.
and implicitly converting anything that is not numerically to 0 ... so <string> + '.' + <string> is evaluated to 0 + 0 + 0

glad I could help

20120131-EE-VQP-002

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