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 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. 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.