Performance Schema Summary Tables • events_errors_summary_global_by_error : •Primary key on ( ERROR_NUMBER ) •For summary tables not aggregated by account, host, or user, truncation resets the summary columns to zero or  NULL  rather than removing rows. •For summary tables aggregated by account, host, or user, truncation removes rows for accounts, hosts, or users with no connections, and resets the summary columns to zero or  NULL  for the remaining rows. TRUNCATE TABLE  is permitted for error summary tables. It has these effects: In addition, each error summary table that is aggregated by account, host, user, or thread is implicitly truncated by truncation of the connection table on which it depends, or truncation of events_errors_summary_global_by_error . For details, see Section 27.12.8, “Performance Schema Connection Tables” . The Performance Schema makes status variable information available in the tables described in Section 27.12.15, “Performance Schema Status Variable Tables” . It also makes aggregated status variable information available in summary tables, described here. Each status variable summary table has one or more grouping columns to indicate how the table aggregates status values: • status_by_account  has  USER ,  HOST , and  VARIABLE_NAME  columns to summarize status variables by account. • status_by_host  has  HOST  and  VARIABLE_NAME  columns to summarize status variables by the host from which clients connected. • status_by_user  has  USER  and  VARIABLE_NAME  columns to summarize status variables by client user name. • VARIABLE_VALUE Each status variable summary table has this summary column containing aggregated values: The aggregated status variable value for active and terminated sessions. The status variable summary tables have these indexes: • status_by_account : • status_by_host : •Primary key on ( HOST ,  VARIABLE_NAME ) •Primary key on ( USER ,  HOST ,  VARIABLE_NAME ) • status_by_user : •Primary key on ( USER ,  VARIABLE_NAME ) The meaning of “account”  in these tables is similar to its meaning in the MySQL grant tables in the  mysql system database, in the sense that the term refers to a combination of user and host values. They differ in that, for grant tables, the host part of an account can be a pattern, whereas for Performance Schema tables, the host value is always a specific nonpattern host name. 5076 27.12.20.12 Status Variable Summary Tables