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Question

I'm using MySql. I got to simplify a query. The (query is just for understanding) original is as bellow:

SELECT id from (SELECT id FROM table ORDER BY C1, C2) ORDER BY C1

This one works fine, takes few seconds.

And the simplified version should be:

SELECT id FROM table ORDER BY C1

But the second query is taking time forever for a large table. Both C1 and C2 are indexed separately.

Please help,

Show index results

Primary id 4312718 candidates

C1 130688 candidates

C2 22 candidates

Answer 1

That is an expected result for large tables. Try using LIMIT 100; or whatever You need.

Answer 2

在MysqL Workbench mysql.com/products/workbench或类似的GUI DB实用程序中运行EXPLIAN，因为它们可以提供很多更好的输出。