Turkbear <john.g_at_dot.spamfree.com> wrote:
>"Dan" <daniel.ostertag_at_visaer.com> wrote:
>
>>I'm trying to put together some general 'best practices' for writing
>>sql queries. I've been reading several books, docs, etc. One thing
>>I've read very little about, but have heard about, is the order of
>>filters in the 'where' clause and whether a field is on the right side
>>or left side of the equal sign.
>>
>>For example, in a query such as
>>select a.xxx, b.yyy, c.zzz from table1 a, table2 b, table3 c
>>where
>> a.aaa = b.bbb and
>> b.aaa = c.ccc and
>> b.ddd = 'XXX';
>>
>>I've read about using the smallest table as the driving table, but
>>other than that, the order of the tables or whether b.aaa=c.ccc or
>>c.ccc=b.aaa is correct, I can find very little about.
>>
>>Does anyone have any info or general rules on this or a reference as to
>>where I could read more (or perhaps tell me it's not important).
>>
>>Thanks,
>>Dan
>
>In general ( and in theory), on an analyzed table(s), The Oracle RBO will find the best method, regardless of the order..
>
>( as an aside,iirc, it is not the 'smallest table' that is always best as the 'driving' one, but the table who's returned
>rows can be reduced as far as possible by the selection criteria..This reduces the # of rows read from the linked tables..)
>
Bad fingers, bad fingers..I meant the CBO ( my fingers are v6)
Received on Thu Oct 20 2005 - 08:37:30 CDT
