19.4.6 The Event Scheduler and MySQL Privileges

To enable or disable the execution of scheduled events, it is necessary to set the value of the global event_scheduler system variable. This requires the SUPER privilege.

MySQL 5.1.6 introduces a privilege governing the creation, modification, and deletion of events, the EVENT privilege. This privilege can be bestowed using GRANT. For example, this GRANT statement confers the EVENT privilege for the schema named myschema on the user jon@ghidora:

GRANT EVENT ON myschema.* TO jon@ghidora;

(We assume that this user account already exists, and that we wish for it to remain unchanged otherwise.)

To grant this same user the EVENT privilege on all schemas, use the following statement:

GRANT EVENT ON *.* TO jon@ghidora;

The EVENT privilege has global or schema-level scope. Therefore, trying to grant it on a single table results in an error as shown:

mysql> GRANT EVENT ON myschema.mytable TO jon@ghidora;
ERROR 1144 (42000): Illegal GRANT/REVOKE command; please
consult the manual to see which privileges can be used

It is important to understand that an event is executed with the privileges of its definer, and that it cannot perform any actions for which its definer does not have the requisite privileges. For example, suppose that jon@ghidora has the EVENT privilege for myschema. Suppose also that this user has the SELECT privilege for myschema, but no other privileges for this schema. It is possible for jon@ghidora to create a new event such as this one:

CREATE EVENT e_store_ts
    ON SCHEDULE
      EVERY 10 SECOND
    DO
      INSERT INTO myschema.mytable VALUES (UNIX_TIMESTAMP());

The user waits for a minute or so, and then performs a SELECT * FROM mytable; query, expecting to see several new rows in the table. Instead, the table is empty. Since the user does not have the INSERT privilege for the table in question, the event has no effect.

If you inspect the MySQL error log (hostname.err), you can see that the event is executing, but the action it is attempting to perform fails, as indicated by RetCode=0:

060209 22:39:44 [Note]     EVEX EXECUTING event newdb.e [EXPR:10]
060209 22:39:44 [Note]     EVEX EXECUTED event newdb.e  [EXPR:10]. RetCode=0
060209 22:39:54 [Note]     EVEX EXECUTING event newdb.e [EXPR:10]
060209 22:39:54 [Note]     EVEX EXECUTED event newdb.e  [EXPR:10]. RetCode=0
060209 22:40:04 [Note]     EVEX EXECUTING event newdb.e [EXPR:10]
060209 22:40:04 [Note]     EVEX EXECUTED event newdb.e  [EXPR:10]. RetCode=0

Since this user very likely does not have access to the error log, it is possible to verify whether the event's action statement is valid by executing it directly:

mysql> INSERT INTO myschema.mytable VALUES (UNIX_TIMESTAMP());
ERROR 1142 (42000): INSERT command denied to user
'jon'@'ghidora' for table 'mytable'

Inspection of the INFORMATION_SCHEMA.EVENTS table shows that e_store_ts exists and is enabled, but its LAST_EXECUTED column is NULL:

mysql> SELECT * FROM INFORMATION_SCHEMA.EVENTS
     >     WHERE EVENT_NAME='e_store_ts'
     >     AND EVENT_SCHEMA='myschema'\G
*************************** 1. row ***************************
   EVENT_CATALOG: NULL
    EVENT_SCHEMA: myschema
      EVENT_NAME: e_store_ts
         DEFINER: jon@ghidora
      EVENT_BODY: SQL
EVENT_DEFINITION: INSERT INTO myschema.mytable VALUES (UNIX_TIMESTAMP())
      EVENT_TYPE: RECURRING
      EXECUTE_AT: NULL
  INTERVAL_VALUE: 5
  INTERVAL_FIELD: SECOND
        SQL_MODE: NULL
          STARTS: 0000-00-00 00:00:00
            ENDS: 0000-00-00 00:00:00
          STATUS: ENABLED
   ON_COMPLETION: NOT PRESERVE
         CREATED: 2006-02-09 22:36:06
    LAST_ALTERED: 2006-02-09 22:36:06
   LAST_EXECUTED: NULL
   EVENT_COMMENT:
1 row in set (0.00 sec)
Note

Prior to MySQL 5.1.12, there was no EVENT_DEFINITION column, and EVENT_BODY contained the SQL statement or statements to be executed. See Section 20.7, “The INFORMATION_SCHEMA EVENTS Table”, for more information.

To rescind the EVENT privilege, use the REVOKE statement. In this example, the EVENT privilege on the schema myschema is removed from the jon@ghidora user account:

REVOKE EVENT ON myschema.* FROM jon@ghidora;
Important

Revoking the EVENT privilege from a user does not delete or disable any events that may have been created by that user.

An event is not migrated or dropped as a result of renaming or dropping the user who created it.

Suppose that the user jon@ghidora has been granted the EVENT and INSERT privileges on the myschema schema. This user then creates the following event:

CREATE EVENT e_insert
    ON SCHEDULE
      EVERY 7 SECOND
    DO
      INSERT INTO myschema.mytable;

After this event has been created, root revokes the EVENT privilege for jon@ghidora. However, e_insert continues to execute, inserting a new row into mytable each seven seconds. The same would be true if root had issued either of these statements:

You can verify that this is true by examining the mysql.event table (discussed later in this section) or the INFORMATION_SCHEMA.EVENTS table (see Section 20.7, “The INFORMATION_SCHEMA EVENTS Table”) before and after issuing a DROP USER or RENAME USER statement.

Event definitions are stored in the mysql.event table, which was added in MySQL 5.1.6. To drop an event created by another user account, the MySQL root user (or another user with the necessary privileges) can delete rows from this table. For example, to remove the event e_insert shown previously, root can use the following statement:

DELETE FROM mysql.event
    WHERE db = 'myschema'
      AND definer = 'jon@ghidora'
      AND name = 'e_insert';

It is very important to match the event name, database schema name, and user account when deleting rows from the mysql.event table. This is because the same user can create different events of the same name in different schemas.

Note

The namespace for scheduled events changed in MySQL 5.1.12. Prior to that MySQL version, different users could create different events having the same name in the same database; in MySQL 5.1.12 and later, that is no longer the case. When upgrading to MySQL 5.1.12 or later from MySQL 5.1.11 or earlier, it is extremely important to make sure that no events in the same database share the same name, prior to performing the upgrade.

Users' EVENT privileges are stored in the Event_priv columns of the mysql.user and mysql.db tables. In both cases, this column holds one of the values 'Y' or 'N'. 'N' is the default. mysql.user.Event_priv is set to 'Y' for a given user only if that user has the global EVENT privilege (that is, if the privilege was bestowed using GRANT EVENT ON *.*). For a schema-level EVENT privilege, GRANT creates a row in mysql.db and sets that row's Db column to the name of the schema, the User column to the name of the user, and the Event_priv column to 'Y'. There should never be any need to manipulate these tables directly, since the GRANT EVENT and REVOKE EVENT statements perform the required operations on them.

MySQL 5.1.6 introduces five status variables providing counts of event-related operations (but not of statements executed by events; see Section D.1, “Restrictions on Stored Programs”). These are:

You can view current values for all of these at one time by running the statement SHOW STATUS LIKE '%event%';.