CODEWITHSUNDEEP
sqltableau-api
Rahul Diggi
Rahul Diggi

Reputation: 430

Custom SQL Query in Tableau

Does using 'custom SQL' instead of joins in Tableau increase the performance of extract refresh on the server? Can someone explain it briefly?

Upvotes: 3

Views: 1692

Answers (1)

Alex Blakemore
Alex Blakemore

Reputation: 11896

The answer to almost every performance question is first, "it depends" and second, test and understand the measurement results. Real results carry more weight than advice from anyone on the Internet (from me or anyone else)

Still, custom SQL is usually not helpful for increasing performance in Tableau, and often hurts. It is usually much better to define your relationships in Tableau and let Tableau then generate optimized SQL for each view -- just as you let a compiler generate optimized machine code.

When you use custom SQL, you prevent Tableau from optimizing the SQL it generates. It has to run the SQL you provide in a subquery.

The best use case for custom SQL in Tableau is to access database specific features, or possibly windowing queries. Most other SQL functionality is available by using the corresponding Tableau features.

If you do have a complex slow custom SQL query that you must use, it is usually a good idea to make an extract so you only pay the performance cost during extract refresh.

So in your case, I'd focus effort on streamlining or eliminating the custom SQL, monitoring the query plan for the generated SQL, and indexing your database to best support that query.

Upvotes: 1

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