There is plenty of documentation on these commands which I suggest reading,
but to summarise obscenely...
These options can be used to analyze just certain elements whilst leaving
other statistics unchanged. If you rebuilt the indexes on a table you
might want to simply "analyze table blah for all indexes" just to gather
stats on the indexes. Also, they can be used to create histograms.
Histograms report on the distribution of data. Say you have an index on
gender and 99% of the records were male.... Summing the age of all males
would be best done using a full table scan, summing the females may be
better by using the index and single row lookups. Without a histogram the
optimisor would have said "only 2 distinct values so scan the tables for
females too" not knowing how rare a female record is in the table.
Warning - histograms (from my really brief description) sound really good
and you may ask yourself "why not create them everywhere". They aren't
that good except in specific instances. In other scenario's they just slow
the optimisor down (while it scans the histogram) and provide no benefit.
You need to learn "when" to use a histogram.
Regards,
Mark.
"quriyat "
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Sent by: Subject: Analyze - For All option
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17/10/2003 09:54
Please respond to
ORACLE-L
Hi List
Can anyone enlighten me on the diff between
ANALYZE TABLE COMPUTE STATISTICS
--AND--
analyze table my_emp compute statistics for table for all indexes
for all indexed columns;
TIA
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