Msg: 2116, Level: 16, State: 1
CREATE TRIGGER failed because selecting from a TEXT, IMAGE, UNITEXT or off-row Java datatype column of the inserted or deleted table is not supported.
Explanation:
Starting with ASE 15.0.3 ESD 4, 15.5 ESD 2, and 15.7, ASE started raising error 2116 if the code for a CREATE TRIGGER attempted to reference a LOB (text, image, unitext) column from the trigger's inserted or deleted tables. Such triggers could be created in earlier versions, but selecting text or image data from the inserted/deleted pseudotables in triggers has never actually been supported. The documentation has always stated that it cannot be done although ASE hasn't previously enforced the restriction; that the code works in some cases is accidental. The main reason for starting to enforce the restriction came from misleading 10785 errors being raised when text/image was accessed using the new "INSTEAD OF" trigger feature against views (CR 590800), but we realized the issue was generic to all triggers.
The core issue is that the inserted and deleted tables are essentially views of the data row change records from syslogs, but do not include the records containing the text/image values themselves. The data returned for the text/image values does not come from the log because that access method was never designed or implemented; rather ASE is just using the textptr value from the inserted or deleted row in syslogs as it would for a regular table. As a result it accesses the current contents of the page the textptr points to rather than the data for the LOB value in the log records..
That is why the following example returns "after" when it should return "before" - it is reading the text value from the data page accessed through the textptr (the textptr generally does not actually change when the value is updated, ASE reuses the existing allocations for the new value and allocates more pages if needed).
select @@version
go
create table t (x text)
go
create trigger utrig on t for update as
select x as "value_from_inserted" from inserted
select x as "value from_deleted" from deleted
go
insert t values ("before")
go
update t set x = "after"
go
Adaptive Server Enterprise/15.0.3/EBF 16736 ESD#2/P/Sun_svr4/OS 5.8/ase1503/270 7/64-bit/FBO/Sun Jul 26 10:29:50 2009
value_from_inserted
---------------------------------
after
(1 row affected)
value from_deleted
---------------------------------
after
(1 row affected)
logically, this result should be "before" - but as described above the text/image values aren’t supported.
Another example of a problem when selecting text/image from deleted is that
error 7128 is raised if the trigger was on DELETE.
create trigger deltrig on t for delete
as select x from deleted where x like '%'
go
delete t
go
Msg 7128, Level 16, State 3:
Server 'bret_sun2', Procedure 'deltrig', Line 7:
Text pointer value 0x0000036a000000000000000000001b18 references a data page which is no longer allocated. This text pointer references first text page 874, which belongs to object ID 1273872784.
x
---------------------------------
(0 rows affected)
The supported way to get the new text/image value is to select the value from the user table (rather than inserted) by joining with inserted on the primary key.
e.x. rather than
create trigger mytrigger on mytable for insert, update
as
insert text_archive select text_col from inserted
go
write the code as
create trigger mytrigger on mytable for insert, update
as
insert text_archive select m.text_col
from mytable m, inserted i
where m.primarykeycol = i.primarykeycol
go
There is no direct supported way to get the deleted or pre-update value, though user code can be written to explicitly archive the value before updating or deleting it.
There is an indirect method to access the old value that is supportable, but it is cumbersome and doubles the amount of storage needed for the text/image values. That method is to create a shadow table that contains the primary key of the base table and a copy of the text/image value. Initially populate this shadow table by inserting into it the current values in the base table. Then on the base table, the triggers should contain logic to maintain the shadow table:
- insert trigger: should insert the new values to the shadow table
- delete trigger: user code that needs to access the old value can get it from the shadow table referenced by the primary key. The trigger should then finish up by deleting the row from the shadow table.
- update trigger: user code that needs to access the old value can get it from the shadow table referenced by the primary key. The trigger should then finish up by updating the text/image values in the shadow table with the current value from the base table.
The enforcement of the restriction can be removed by booting ASE with traceflag 1716 (put -T1716 in the dataserver parameter list in the RUN_SERVER file). This will give the same behavior as pre-15.0.3 ESD 4 versions (including the errors and incorrect results when selecting from deleted).
There is an open feature request 593730 to formally support text/image values in triggers.