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SQL Anywhere 11.0.1 (Français) » SQL Anywhere Server - SQL Reference » Using SQL » SQL statements » SQL statements (A-D)

 

CREATE EVENT statement

Use this statement to define an event and its associated handler for automating predefined actions, and to define scheduled actions.

Syntax
CREATE EVENT [ owner.]event-name
[ TYPE event-type
         [ WHERE trigger-condition [ AND trigger-condition ] ... ]
    | SCHEDULE schedule-spec, ... ]
[ ENABLE | DISABLE ]
[ AT { CONSOLIDATED | REMOTE | ALL } ]
[ HANDLER
      BEGIN
...
     END ]
event-type :
  BackupEnd 
| Connect
| ConnectFailed 
| DatabaseStart
| DBDiskSpace
| Deadlock 
| "Disconnect"
| GlobalAutoincrement 
| GrowDB
| GrowLog 
| GrowTemp
| LogDiskSpace 
| MirrorFailover
| MirrorServerDisconnect 
| RAISERROR
| ServerIdle 
| TempDiskSpace
trigger-condition :
event_condition( condition-name ) { 
= 
| < 
| > 
| != 
| <= 
| >= 
} value
schedule-spec :
[ schedule-name ]
   { START TIME start-time | BETWEEN start-time AND end-time }
   [ EVERY period { HOURS | MINUTES | SECONDS } ]
   [ ON { ( day-of-week, ... ) | ( day-of-month, ... ) } ]
   [ START DATE start-date ]
event-name : identifier
schedule-name : identifier
day-of-week : string
day-of-month : integer
value : integer
period : integer
start-time : time
end-time : time
start-date : date
Parameters
  • CREATE EVENT clause   The event name is an identifier. An event has a creator, which is the user creating the event, and the event handler executes with the permissions of that creator. This is the same as stored procedure execution. You cannot create events owned by other users.

  • TYPE clause   You can specify the TYPE clause with an optional WHERE clause; or specify the SCHEDULE.

    The event-type is one of the listed set of system-defined event types. The event types are case insensitive. To specify the conditions under which this event-type triggers the event, use the WHERE clause. For a description of event-types not listed below, see Understanding system events.

    • DiskSpace event types   If the database contains an event handler for one of the DiskSpace types, the database server checks the available space on each device associated with the relevant file every 30 seconds.

      In the event the database has more than one dbspace, on separate drives, DBDiskSpace checks each drive and acts depending on the lowest available space.

      The LogDiskSpace event type checks the location of the transaction log and any transaction log mirror, and reports based on the least available space.

      Disk space event types are not supported on Windows Mobile.

      The TempDiskSpace event type checks the amount of temporary disk space.

      If the appropriate event handlers have been defined (DBDiskSpace, LogDiskSpace, or TempDiskSpace), the database server checks the available space on each device associated with a database file every 30 seconds. Similarly, if an event has been defined to handle the system event type ServerIdle, the database server notifies the handler when no requests have been process during the previous 30 seconds.

      You can specify the -fc option when starting the database server to implement a callback function when the database server encounters a file system full condition.

      See -fc server option.

    • GlobalAutoIncrement event type   The event fires on each insert when the number of remaining values for a GLOBAL AUTOINCREMENT is less than 1% of the end of its range. A typical action for the handler could be to request a new value for the global_database_id option, based on the table and number of remaining values which are supplied as parameters to this event.

      You can use the event_condition function with RemainingValues as an argument for this event type.

    • ServerIdle event type   If the database contains an event handler for the ServerIdle type, the database server checks for server activity every 30 seconds.

    • Database mirroring event types   The MirrorServerDisconnect event fires when a connection from the primary database server to the mirror server or arbiter server is lost, and the MirrorFailover event fires whenever a server takes ownership of the database. See Database mirroring system events.

  • WHERE clause   The trigger condition determines the condition under which an event is fired. For example, to take an action when the disk containing the transaction log becomes more than 80% full, use the following triggering condition:
    ...
    WHERE event_condition( 'LogDiskSpacePercentFree' ) < 20
    ...

    The argument to the event_condition function must be valid for the event type.

    You can use multiple AND conditions to make up the WHERE clause, but you cannot use OR conditions or other conditions.

    For information about valid arguments, see EVENT_CONDITION function [System].

  • SCHEDULE clause   This clause specifies when scheduled actions are to take place. The sequence of times acts as a set of triggering conditions for the associated actions defined in the event handler.

    You can create more than one schedule for a given event and its associated handler. This permits complex schedules to be implemented. While it is compulsory to provide a schedule-name when there is more than one schedule, it is optional if you provide only a single schedule.

    A scheduled event is recurring if its definition includes EVERY or ON; if neither of these reserved words is used, the event will execute at most once. An attempt to create a non-recurring scheduled event for which the start time has passed will generate an error. When a non-recurring scheduled event has passed, its schedule is deleted, but the event handler is not deleted.

    Scheduled event times are calculated when the schedules are created, and again when the event handler completes execution. The next event time is computed by inspecting the schedule or schedules for the event, and finding the next schedule time that is in the future. If an event handler is instructed to run every hour between 9:00 and 5:00, and it takes 65 minutes to execute, it runs at 9:00, 11:00, 1:00, 3:00, and 5:00. If you want execution to overlap, you must create more than one event.

The subclauses of a schedule definition are as follows:

  • START TIME clause   The first scheduled time for each day on which the event is scheduled. The start-time parameter is a string, and cannot be a variable or an expression such as NOW(). If a START DATE is specified, the START TIME refers to that date. If no START DATE is specified, the START TIME is on the current day (unless the time has passed) and each subsequent day (if the schedule includes EVERY or ON).

  • BETWEEN ... AND clause   A range of times during the day outside which no scheduled times occur. The start-time and end-time parameters are strings, and cannot be variables or expressions such as NOW(). If a START DATE is specified, the scheduled times do not occur until that date.

  • EVERY clause   An interval between successive scheduled events. Scheduled events occur only after the START TIME for the day, or in the range specified by BETWEEN ... AND.

  • ON clause   A list of days on which the scheduled events occur. The default is every day if EVERY is specified. Days can be specified as days of the week or days of the month.

    Days of the week are Mon, Tues, and so on. You may also use the full forms of the day, such as Monday. You must use the full forms of the day names if the language you are using is not English, is not the language requested by the client in the connection string, and is not the language which appears in the database server messages window.

    Days of the month are integers from 0 to 31. A value of 0 represents the last day of any month.

  • START DATE clause   The date on which scheduled events are to start occurring. This value is a string, and cannot be a variable or an expression such as TODAY(). The default is the current date.

    Each time a scheduled event handler is completed, the next scheduled time and date is calculated.

    1. If the EVERY clause is used, find whether the next scheduled time falls on the current day, and is before the end of the BETWEEN ... AND range. If so, that is the next scheduled time.

    2. If the next scheduled time does not fall on the current day, find the next date on which the event is to be executed.

    3. Find the START TIME for that date, or the beginning of the BETWEEN ... AND range.

  • ENABLE | DISABLE clause   By default, event handlers are enabled. When DISABLE is specified, the event handler does not execute even when the scheduled time or triggering condition occurs. A TRIGGER EVENT statement does not cause a disabled event handler to be executed.

  • AT clause   This clause should be used only in the following circumstance: in a SQL Remote setup, use the AT clause against your remote or consolidated databases to restrict the databases at which the event is handled.

    If you do not use the AT clause when creating events for SQL Remote, all databases execute the event. When executed on a consolidated database, this statement will not affect remote databases that have already been extracted.

  • HANDLER clause   Each event has one handler.

Remarks

Events can be used in two main ways:

  • Scheduling actions   The database server executes actions on a timed schedule. You can use this capability to complete scheduled tasks such as backups, validity checks, and queries used to add data to reporting tables.

  • Event handling actions   The database server executes actions when a predefined event occurs. You can use this capability to complete scheduled tasks such as restrict disk space when a disk fills beyond a specified percentage. Event handler actions are committed if errors are not detected during execution, and rolled back if errors are detected.

An event definition includes two distinct pieces. The trigger condition can be an occurrence, such as a disk filling up beyond a defined threshold. A schedule is a set of times, each of which acts as a trigger condition. When a trigger condition is satisfied, the event handler executes. The event handler includes one or more actions specified inside a compound statement (BEGIN... END).

If no trigger condition or schedule specification is supplied, only an explicit TRIGGER EVENT statement can trigger the event. During development, you may want to test event handlers using TRIGGER EVENT, and add the schedule or WHERE clause once testing is complete.

Event errors are logged to the database server message log. See Logging database server actions.

After each execution of an event handler, a COMMIT occurs if no errors occurred. A ROLLBACK occurs if there was an error.

When event handlers are triggered, the database server makes context information, such as the connection ID that caused the event to be triggered, available to the event handler using the event_parameter function. For more information about event_parameter, see EVENT_PARAMETER function [System].

Permissions

Must have DBA authority.

Event handlers execute on a separate connection, with the permissions of the event owner. To execute with authority other than DBA, you can call a procedure from within the event handler: the procedure executes with the permissions of its owner. The separate connection does not count towards the ten-connection limit of the personal database server.

Side effects

Automatic commit.

See also
Standards and compatibility
  • SQL/2003   Vendor extension.

Example

Instruct the database server to carry out an automatic backup to tape using the first tape drive, every day at 1 A.M.

CREATE EVENT DailyBackup
SCHEDULE daily_backup
START TIME '1:00AM' EVERY 24 HOURS
HANDLER
   BEGIN
      BACKUP DATABASE TO '\\\\.\\tape0'
      ATTENDED OFF
   END;

Instruct the database server to carry out an automatic backup of the transaction log only, every hour, Monday to Friday between 8 A.M. and 6 P.M.

CREATE EVENT HourlyLogBackup
SCHEDULE hourly_log_backup
BETWEEN '8:00AM' AND '6:00PM'
EVERY 1 HOURS ON
   ('Monday','Tuesday','Wednesday','Thursday','Friday')
HANDLER
   BEGIN
      BACKUP DATABASE DIRECTORY 'c:\\database\\backup'
      TRANSACTION LOG ONLY
      TRANSACTION LOG RENAME
   END;

See Defining trigger conditions for events.