SQL Troubleshooter "4" to avoid subqueries when querying large amounts of data

Source: Internet
Author: User

The previous few days found that the system became very slow, in the profiler found some SQL executed for a few 10 seconds to return the results, then the SQL is as follows:

As you can see, the subquery is used in 652 rows, and the number of records in the target table (QS_WIP) is 100000000 +, which can be obtained by the following SQL:

SELECT ROWS from sysindexes WHERE id=object_id (' Qs_wip ') and indid <2

A large number of data results in a very slow sub-query, the application system once prompted "time out", after optimization, to the following wording, the execution efficiency significantly improved:

First, the contents of the subquery are extracted as a temporary table, once again join the time is fast.

SQL Troubleshooter "4" to avoid subqueries when querying large amounts of data

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