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Rob
Rob

Reputation: 7217

Sqlite - efficient select count query

I have a table in my database I do a Select all on: 

SELECT * FROM TableA;

I want to append a column that is true or false if there's a related column in anther table. I can do it with this:

SELECT *, (SELECT COUNT(Id) > 0 FROM TableB WHERE Id = TableA.Id) FROM TableA;

But I don't want to have to count EVERY row in TableB to work this out as its ineffient. I essentially want an EXISTS check instead of count.

How do I replace the COUNT with EXISTS?

Thanks!

Upvotes: 0

Views: 104

Answers (2)

Rob
Rob

Reputation: 7217

Ah - just realised the answer to my own question

SELECT *, EXISTS(SELECT Id FROM TableB WHERE Id= TableA.Id) AS DoesExist FROM TableA

Upvotes: 1

juergen d
juergen d

Reputation: 204766

By using a left join

SELECT a.*, b.id is not null as condition_check
FROM TableA a
LEFT JOIN TableB b ON a.Id = b.Id

Upvotes: 1

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