How would you go about optimizing a sluggish SQL query?

Question

Anonymous · Accepted Answer

SQL is not as easy to debug as standard programming languages due to it being
more declarative and less room for minute optimizations. But we can still apply
standard techniques.

1. 1. First, if this is a large query, break it into smaller parts and
    investigate which part is slow. Once you get to a single subquery,

2. 2. Next, investigate your main operations (usually a join of some kind). Can
    you

3. 1. Filter before joining?

4. 2. Remove columns you do not need

5. 3. Remove temporary tables you don't need (maybe less important for SQL
    proper but in Spark type applications very important)?

6. 4. Choose other tables that would do the job. Or choose which tables to join
    first and then filter and then do the other joins. If the output is expected
    going to be relatively small, there's a good chance you can filter and
    optimize table join orders to reduce time.

Anonymous · Answer

I would look to see if i could use a smaller table. Then I would look to see if
there are any joins and if there are can i be more stringent with the joining
conditions. I would select fewer columns or only those that are necessary.

How would you go about optimizing a sluggish SQL query?

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