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MySQL 8.0 Reference Manual
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MySQL 8.0 Reference Manual/.../ Obtaining Execution Plan Information for a Named Connection

8.8.4 Obtaining Execution Plan Information for a Named Connection

To obtain the execution plan for an explainable statement executing in a named connection, use this statement:

EXPLAIN [options] FOR CONNECTIONconnection_id;

EXPLAIN FOR CONNECTIONreturns theEXPLAINinformation that is currently being used to execute a query in a given connection. Because of changes to data (and supporting statistics) it may produce a different result from runningEXPLAINon the equivalent query text. This difference in behavior can be useful in diagnosing more transient performance problems. For example, if you are running a statement in one session that is taking a long time to complete, usingEXPLAIN FOR CONNECTIONin another session may yield useful information about the cause of the delay.

connection_idis the connection identifier, as obtained from the正ORMATION_SCHEMAPROCESSLISTtable or theSHOW PROCESSLISTstatement. If you have thePROCESSprivilege, you can specify the identifier for any connection. Otherwise, you can specify the identifier only for your own connections. In all cases, you must have sufficient privileges to explain the query on the specified connection.

If the named connection is not executing a statement, the result is empty. Otherwise,EXPLAIN FOR CONNECTIONapplies only if the statement being executed in the named connection is explainable. This includesSELECT,DELETE,INSERT,REPLACE, andUPDATE. (However,EXPLAIN FOR CONNECTIONdoes not work for prepared statements, even prepared statements of those types.)

If the named connection is executing an explainable statement, the output is what you would obtain by usingEXPLAINon the statement itself.

If the named connection is executing a statement that is not explainable, an error occurs. For example, you cannot name the connection identifier for your current session becauseEXPLAINis not explainable:

mysql> SELECT CONNECTION_ID(); +-----------------+ | CONNECTION_ID() | +-----------------+ | 373 | +-----------------+ 1 row in set (0.00 sec) mysql> EXPLAIN FOR CONNECTION 373; ERROR 1889 (HY000): EXPLAIN FOR CONNECTION command is supported only for SELECT/UPDATE/INSERT/DELETE/REPLACE

TheCom_explain_otherstatus variable indicates the number ofEXPLAIN FOR CONNECTIONstatements executed.