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Asked: 2026-06-02T07:43:48+00:00

I am using QSQlQuery on a sqlite3 database. To fetch a particular item ,

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I am using QSQlQuery on a sqlite3 database. To fetch a particular item , I was populating the result from 4 different tables. I thought joining the tables would increase the performance/speed and get the result faster. So I joined 2 tables initially but it takes longer time to fetch the data after joining the tables (?)

Any suggestion on how to improve the performance would be really appreciated. Also, I was looking at the http://qt-project.org/doc/qt-4.8/qsqlquery.html and it is mentioned that using setForwardOnly would increase the performance on some databases. Any idea if it would work for SQLite3?

Thanks!

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1 Answer

  1. Editorial Team

    According to this link,

    http://sqlite.org/cvstrac/wiki?p=PerformanceTuning

    SQLite implements JOIN USING by translating the USING clausing into some extra WHERE clause terms. It does the same with NATURAL JOIN and JOIN ON. So while those constructs might be helpful to the human reader, they don’t really make any difference to SQLite’s query optimizer.

    -I was wrong to join two tables and expect the fetch to be faster. It does not work with SQLite database. Instead using a “where” clause and joining two results directly definitely has some positive impact on the performance.

    (example :

    select * from A,B where A.id = B.id where A.id = 1; instead of

    select * from A left outer join B on A.id = B.id where A.id = 1)

    The SQLite translates first statement to second before compiling and you could save on the small amount of CPU time by directly using the second statement

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