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Strange SQL Speed
Message
From
18/10/2000 14:49:34
 
 
General information
Forum:
Visual FoxPro
Category:
Other
Miscellaneous
Thread ID:
00431066
Message ID:
00431070
Views:
12
>In VFP 6, two free tables, table1 (739,068 records) and table2 (609,862 records) each has a fieldx which is a 7 byte long character representation of a number which is unique within each table. Each table has an index tag on fieldx. The following:
>
>SELECT fieldx FROM table2 WHERE fieldx NOT IN (SELECT fieldx FROM table1)

Try following query:

SELECT fieldx FROM table2 WHERE NOT EXISTS (SELECT fieldx FROM table1 where table1.fieldx=table2.fieldx)

If table1 and table2 indexed by fieldx field, you should have good speed.


>
>This correctly return 31,183 records in 1002.50 seconds.
>
>SELECT fieldx FROM table1 INTO CURSOR tab1 NOFI
>SELECT fieldx FROM table2 INTO CURSOR tab2 NOFI
>SELECT fieldx FROM tab2 WHERE fieldx NOT IN (SELECT fieldx FROM tab1)
>
>This correctly return 31,183 records in 25.60 seconds.
>
>Before each run I made sure that VFP was the only process running on the Windows 95 machine. Pretty strange.
Vlad Grynchyshyn, Project Manager, MCP
vgryn@yahoo.com
ICQ #10709245
The professional level of programmer could be determined by level of stupidity of his/her bugs

It is not appropriate to say that question is "foolish". There could be only foolish answers. Everybody passed period of time when knows nothing about something.
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