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MySQL Query unique field but only when there is no double entry?

MySQL Query unique field but only when there is no double entry

Hi im not a native speaker and im not into sql language. I can do some standard queries like select * from table... update and so on but have no expierience in deeper sql questions.

plz	ort	gemeinde
1000	uttenthal	buchkirchen
1000	buchkirchen	buchkirchen
2000	mistelbach	buchkirchen
2000	unterholz	buchkirchen

I have a table like this and need to get a list of plz where ort <> gemeinde but only when there is no case where ort=gemeinde for this plz.

In this example i only should get plz 2000 because there exists a entry where ort buchkirchen = gemeinde buchkirchen for plz 1000.

Solution:

You can use Not Exists

select plz from table t1 
where not exists
(select 1 from table t2 where t1.plz = t2.plz and ort = gemenide)

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MySQL Query unique field but only when there is no double entry, sql, mysql

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