# SQL statistics for Performance Insights
<a name="sql-statistics"></a>

*SQL statistics* are performance-related metrics about SQL queries that are collected by Performance Insights. Performance Insights gathers statistics for each second that a query is running and for each SQL call. The SQL statistics are an average for the selected time range.

A SQL digest is a composite of all queries having a given pattern but not necessarily having the same literal values. The digest replaces literal values with a question mark. For example, `SELECT * FROM emp WHERE lname= ?`. This digest might consist of the following child queries:

```
SELECT * FROM emp WHERE lname = 'Sanchez'
SELECT * FROM emp WHERE lname = 'Olagappan'
SELECT * FROM emp WHERE lname = 'Wu'
```

All engines support SQL statistics for digest queries.

For the region, DB engine, and instance class support information for this feature, see [Amazon RDS DB engine, Region, and instance class support for Performance Insights features](USER_PerfInsights.Overview.Engines.md#USER_PerfInsights.Overview.PIfeatureEngnRegSupport)

**Topics**
+ [SQL statistics for MariaDB and MySQL](USER_PerfInsights.UsingDashboard.AnalyzeDBLoad.AdditionalMetrics.MySQL.md)
+ [SQL statistics for Amazon RDS for Oracle](USER_PerfInsights.UsingDashboard.AnalyzeDBLoad.AdditionalMetrics.Oracle.md)
+ [SQL statistics for Amazon RDS for SQL Server](USER_PerfInsights.UsingDashboard.AnalyzeDBLoad.AdditionalMetrics.SQLServer.md)
+ [SQL statistics for RDS PostgreSQL](USER_PerfInsights.UsingDashboard.AnalyzeDBLoad.AdditionalMetrics.PostgreSQL.md)