in general, you'll see two ways to do this.
you can use a
SELECT * FROM TABLE1 WHERE [Client ID] in (SELECT [Client ID] FROM TABLE2 WHERE Trading_Code IN('ZBwhatever') )
or you can left outer join the table
SELECT * FROM TABLE1
LEFT OUTER JOIN TABLE2 ON TABLE1.[Client ID]=TABLE1.[Client ID]
WHERE WHERE TABLE2 .Trading_Code IN('ZBwhatever')
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