> If you see SQL where someone wrote a SELECT and is then using a cursor to loop through those results and do other queries, you've found the person who is still thinking imperatively.
To a first approximation, yes. But 'client-side joins' can be a valuable tool when the database engine won't cooperate. For some queries and some engines, you can do a select with a join to get everything you need in one query, but a select to get a list of ids followed by a union of selects (not an IN query) to get details for each id will have the results at the client sooner, with less load on the database, at some potential loss of consistency. Your client needs to be within a reasonable round trip of the server or the two queries approach won't get the answer faster.
I'm not sure I follow. Fetching the data in one query should almost always be faster and more efficient - the same work is being done regardless, except now you have the additional overhead involved with a second query (network and connection overhead, parsing etc.)
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