var sidebar_align = 'right';
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Unanswered: Which can give better performance ? Union or Select
Good day All,
i wonder in following sample, which give better performance and why ?
(Select columnB where table_B where condition) AS columnB
FROM table_A A
In above sample, which actually give a better performance ? and any specific reason ?
NULL as ColumnB,
Select null as columnA,
B.column as ColumnB,
FROM table_B B
i wish to learn performance tuning, is there any good reference or booko on this topic ? appreciated your guidance in advance
neither of them will actually compile.
nor would either of them return the same results if you did get them to compile.
and I suspect you probably want to do neither of these.
I would start by looking at JOIN syntax, as well as the difference between UNION and UNION ALL.
EDIT - removed the reference to INNER JOINs - now just referring to JOINs in general
Last edited by pootle flump; 10-15-08 at 11:57.
ur codings are working excelent.