SQL – HAVING vs. WHERE

WHERE clause introduces a condition on individual rows; HAVING clause introduces a condition on aggregations, i.e. results of selection where a single result, such as count, average, min, max, or sum, has been produced from multiple rows. Your query calls for a second kind of condition (i.e. a condition on an aggregation) hence HAVING works correctly. As a rule of thumb, use WHERE before GROUP BY and HAVING after GROUP BY. …

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What is the difference between Scope_Identity(), Identity(), @@Identity, and Ident_Current()?

The @@identity function returns the last identity created in the same session. The scope_identity() function returns the last identity created in the same session and the same scope. The ident_current(name) returns the last identity created for a specific table or view in any session. The identity() function is not used to get an identity, it’s used to create an identity in a select…into query. The …

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Warning: Null value is eliminated by an aggregate or other SET operation in Aqua Data Studio

You would mostly be using COUNT to summarize over a UID. Therefore COUNT([uid]) will produce the warning: Warning: Null value is eliminated by an aggregate or other SET operation. whilst being used with a left join, where the counted object does not exist. Using COUNT(*) in this case would also render incorrect results, as you would then be counting the …

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SQL join on multiple columns in same tables

I have 2 subqueries, but I’m having trouble joining columns together from the same tables. I tried: If I simply end the query with ON a.userid = b.sourceid it works, but how can I also join these tables on another column also ON a.listid = b.destinationid ?? Any help appreciated.

MySQL syntax for Join Update

MySQL supports a multi-table UPDATE syntax, which would look approximately like this: You can update the Train table and delete from the Reservations table in the same transaction. As long as you do the update first and then do the delete second, it should work.