How to implement 'Lookup' in SQL Server Query

I have 2 tables which I want to query to populate a 3rd table with.
Table 1 contains about 1M rows of data.
Table 2 contains a lookup/conversion data i.e col 1 contains a code and col 2 contains meaning.
I am querying table 1 but using table 2 to convert where I find the code to the meaning

Table 2
col 1              col2
code 1           type 1
code 2           type 2
code 3           type 3

So I query table 1 INSERT INTO table 3 (col1, col2, col3, col4) FROM table 1 col 1 col2 (SELECT converted item FROM table 2)...

My problem is that I am getting mutiple rows from the sub query even though all the rows are unique.

What am I doing wrong?
LVL 16
Richard OlutolaConsultantAsked:
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Vitor MontalvãoMSSQL Senior EngineerCommented:
Can you post full query and sample of the records you're getting and what should be expecting?
Richard OlutolaConsultantAuthor Commented:
INSERT INTO TABLE 3 (vref,sledg,tranxdt,ptp)
(SELECT newcode FROM table 2 WHERE table2.oldcode = table1.oldcode),

Table 2 is just a lookup table.

Hope this helps.
Vitor MontalvãoMSSQL Senior EngineerCommented:
You can get rid of the subquery:
INSERT INTO TABLE 3 (vref,sledg,tranxdt,ptp)
SELECT t1.belnr, t2.newcode,  t1.bldat,  t1.monat
    INNER JOIN table2 t2 ON t2.oldcode = t1.oldcode

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Without sample data I can't help much than this.

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Richard OlutolaConsultantAuthor Commented:
That did the trick.
I was close but didn't quite get there.
Many thanks for the quick response too.
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Microsoft SQL Server 2008

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