CREATE EVENT Statement

Syntax

CREATE EVENT 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 
     |  “Disconnect” 
     |  GlobalAutoincrement 
     |  GrowDB  
     |  GrowLog  
     |  GrowTemp   
     |  IQMainDBSpaceFree  
     |  IQTempDBSpaceFree  
     |  LogDiskSpace  
     |  “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 ]

Parameters

event-name – 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. You can list event names by querying the system table SYSEVENT. For example:
```
SELECT event_id, event_name FROM SYS.SYSEVENT
```

event-type – one of a 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.
- DiskSpace – 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.
- LogDiskSpace – checks the location of the transaction log and any mirrored transaction log, and reports based on the least available space.
- Globalautoincrement – fires when the GLOBAL AUTOINCREMENT default value for a table is within one percent of the end of its range. A typical action for the handler could be to request a new value for the GLOBAL_DATABASE_ID clause.
  You can use the EVENT_CONDITION function with RemainingValues as an argument for this event type.
- ServerIdle – if the database contains an event handler for the ServerIdle type, the server checks for server activity every 30 seconds.

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 this 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.

SCHEDULE – 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.
You can list schedule names by querying the system table SYSSCHEDULE. For example:
```
SELECT event_id, sched_name FROM SYS.SYSSCHEDULE
```
Each event has a unique event ID. Use the event_id columns of SYSEVENT and SYSSCHEDULE to match the event to the associated schedule.

When a nonrecurring 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 DATE – the date on which scheduled events are to start occurring. The default is the current date.
- START TIME – the first scheduled time for each day on which the event is scheduled. 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.
- BETWEEN … AND – a range of times during the day outside of which no scheduled times occur. If a START DATE is specified, the scheduled times do not occur until that date.
- EVERY – 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 – a list of days on which the scheduled events occur. The default is every day. These can be specified as days of the week or days of the month.
  Days of the week are Monday, Tuesday, and so on. The abbreviated forms of the day, such as Mon, Tue, and so on, may also be used. The database server recognizes both full-length and abbreviated day names in any of the languages supported by SAP Sybase IQ.
  
  Days of the month are integers from 0 to 31. A value of 0 represents the last day of any month.
Each time a scheduled event handler is completed, the next scheduled time and date is calculated.
- 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.
- If the next scheduled time does not fall on the current day, find the next date on which the event is to be executed.
- Find the START TIME for that date, or the beginning of the BETWEEN … AND range.

ENABLE | DISABLE – 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 – to execute events at remote or consolidated databases in a SQL Remote setup, use this clause to restrict the databases at which the event is handled. By default, all databases execute the event.

HANDLER – each event has one handler. Like the body of a stored procedure, the handler is a compound statement. There are some differences, though: you can use an EXCEPTION clause within the compound statement to handle errors, but not the ON EXCEPTION RESUME clause provided within stored procedures.

Examples

Example 1 – instructs the database server to carry out an automatic incremental backup daily at 1 a.m.:

CREATE EVENT IncrementalBackup
SCHEDULE
START TIME '1:00AM' EVERY 24 HOURS
HANDLER
  BEGIN
    BACKUP DATABASE INCREMENTAL
    TO 'backups/daily.incr'
  END

Example 2 – instructs the database server to call the system stored procedure sp_iqspaceused every 10 minutes, then store in a table the returned current date and time, the current number of connections to the database, and current information about the use of main and temporary IQ store:

CREATE TABLE mysummary(dt DATETIME,
  users INT, mainKB UNSIGNED BIGINT,
  mainPC UNSIGNED INT,
  tempKB UNSIGNED BIGINT,
  tempPC UNSIGNED INT) ;

CREATE EVENT mysummary
  SCHEDULE sched_mysummary
    START TIME '00:01 AM' EVERY 10 MINUTES
  HANDLER
  BEGIN
    DECLARE mt UNSIGNED BIGINT;
    DECLARE mu UNSIGNED BIGINT;
    DECLARE tt UNSIGNED BIGINT;
    DECLARE tu UNSIGNED BIGINT;
    DECLARE conncount UNSIGNED INT;

    SET conncount = DB_PROPERTY('ConnCount');
    CALL SP_IQSPACEUSED(mt,mu,tt,tu);
    
		INSERT INTO mysummary VALUES( NOW(),
    conncount, mu, (mu*100)/mt, tu,
    (tu*100)/tt );
	END;

Example 3 – posts a message to the server log when free disk space on the device containing the transaction log file falls below 30 percent, but execute the handler no more than once every 300 seconds.
```
CREATE EVENT LowTxnLogDiskSpace
TYPE DBDiskSpace
WHERE event_condition( 'DBFreePercent' ) < 30
AND event_condition( 'Interval' ) >= 300
HANDLER
BEGIN
message 'Disk space for Transaction Log is low.';
END;
```

Usage

Events can be used in two main ways:

Scheduling actions – the database server carries out a set of actions on a schedule of times. You can use this capability to schedule backups, validity checks, queries to fill up reporting tables, and so on.
Event handling actions – the database server carries out a set of actions when a predefined event occurs. The events that can be handled include disk space restrictions (when a disk fills beyond a specified percentage), when the server is idle, and so on.

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 might want to develop and 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 console.

When event handlers are triggered, the 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.

Note: Although statements that return result sets are disallowed in events, you can allow an event to call a stored procedure and insert the procedure results into a temporary table.

Side Effects:

Automatic commit.
The actions of an event handler are committed if no error is detected during execution, and rolled back if errors are detected.

Standards

SQL—Vendor extension to ISO/ANSI SQL grammar.
Sybase—Not supported by Adaptive Server Enterprise.

Permissions

Requires one of:

MANAGE ANY EVENT system privilege.
CREATE ANY OBJECT system privilege.

Event handlers execute on a separate connection, with the privileges of the event owner. To execute with privileges other than MANAGE ANY EVENT system privilege, 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.