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SQL Anywhere 10.0.1 » SQL Anywhere Server - SQL Reference » SQL Statements

DROP STATEMENT statement [ESQL] Next Page

DROP STATISTICS statement


Use this statement to erase all column statistics on the specified columns.

Syntax

DROP STATISTICS [ ON ] [owner.]table-name [ ( column-list ) ]

Remarks

The SQL Anywhere optimizer uses column statistics to determine the best strategy for executing each statement. SQL Anywhere automatically gathers and updates these statistics. Column statistics are stored permanently in the database in the ISYSCOLSTAT system table. Column statistics gathered while processing one statement are available when searching for efficient ways to execute subsequent statements.

Occasionally, the column statistics can become inaccurate or relevant statistics may be unavailable. This condition is most likely to arise when few queries have been executed since a large amount of data was added, updated, or deleted.

The DROP STATISTICS statement deletes all internal statistical data from the ISYSCOLSTAT system table for the specified columns. This drastic step leaves the optimizer with no access to essential statistical information. Without these statistics, the optimizer can generate very inefficient data access plans, causing poor database performance.

The DROP STATISTICS statement requires an exclusive lock on the table against which it is being performed. This means that execution of the statement cannot proceed until all other connections that refer to the table have either committed or rolled back the referring transactions, or closed any open cursors that refer to the table.

This statement should be used only during problem determination or when reloading data into a database that differs substantially from the original data.

Permissions

Must have DBA authority.

Side effects

Automatic commit.

See also
Standards and compatibility