UPDATE STATISTICS
Updates
database statistics for query optimization.
SYNTAX
| object_list |
List
of database objects to update statistics data for. |
| number |
Percentage
of data to use when updating statistics data. |
DESCRIPTION
The UPDATE
STATISTICS command updates database statistics information. Keeping statistics
information current helps the database to perform queries more efficiently.
To execute the UPDATE STATISTICS command, you must have DBA or SYSADM
security privileges, or be the owner of the object you are updating statistics
for.
You can
update statistics information for the entire database, or you can take
update statistics information for only one or more tables. For each table,
you can specify whether you want to update the table statistics information,
the column statistics information, the index statistics information, or
a combination of the three. You can also specify the amount of data to
sample as a percentage of the total by specifying a number between 1 and
100 for the SAMPLE keyword.
For table
data, DBMaker records statistics on the number of pages, the number of
rows, and the average row length of sampled rows in a table. For column
data, DBMaker records statistics on the number of distinct column values,
the average column length, the low value, and the high value for all sampled
values in a column. For index data, DBMaker records statistics on the
number of index pages, the number of index tree levels, the number of
leaf pages, the number of distinct key values, the number of pages per
key, and the cluster count for the index.
Object List
EXAMPLE
The following
example updates all statistics information in the database with a sampling
percentage of 30%.
UPDATE STATISTICS SAMPLE = 30
|
The following
example updates all statistics on table1.
UPDATE STATISTICS table1 SAMPLE = 50
|
The following
example updates statistics only for column c1 and index ix1 on table1.
UPDATE STATISTICS table1 (COLUMN (c1) index (ix1))
|
RELATED COMMANDS
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UPDATE | Contents
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