The Table Statistics area of the Analysis tab indicates when and if table statistics were last taken. Using the Table Statistics you can view the information the optimizer uses to choose a path and assess the validity of the various hints presented on the Overview tab.
This table draws attention to:
- Missing statistics: Missing statistics can cause the optimizer to choose the wrong path because the optimizer uses table statistics to make decisions. If the statistics are missing, you can click the select a table and then click Collect Statistics (
) on the far right of the tab. This sends a request to the database to analyze the table and calculate the statistics. Out-of-date statistics: Like missing statistics, out-of-date statistics can also cause the optimizer to choose the wrong path. You can update the statistics by selecting a table, and then clicking Display Statistics (
), which refreshes the statistics from the database or by clicking Collect Statistics (), which requests the database to analyze the table and calculate the statistics.Collecting Statistics may be time-consuming, depending on how many tables the database is analyzing and the number of rows in each table.
Useful statistics: The number of rows in a table and whether the table has been modified since the statistics were last collected can help you to determine which hints you should implement in the SQL code. These statistics can help the DB Administrator to better understand the database.
You can right-click anywhere in a row and choose options such as Collect Statistics, Display Statistics, and Copy from the short-cut menu.