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https://issues.apache.org/jira/browse/DERBY-4874?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12927495#action_12927495
 ] 

Mamta A. Satoor commented on DERBY-4874:
----------------------------------------

I have found what the problem is. The user's definition of trigger is as follows
CREATE TRIGGER mytrig
 AFTER UPDATE ON tab
 REFERENCING NEW AS newt OLD AS oldt
 FOR EACH ROW MODE DB2SQL
  UPDATE tab set tab.counter = CASE WHEN (oldt.counter < 32767) THEN 
(oldt.counter + 1) ELSE 1 END
  WHERE ((newt.counter is null) or (oldt.counter = newt.counter))
  AND newt.element_id = tab.element_id
  AND newt.altered_id = tab.altered_id;

For the trigger action plan, Derby creates a SPSDescriptor which is saved in 
SYS.SYSSTATEMENTS. The above action plan gets converted to following and that 
is the query that is saved in SYS.SYSSTATEMENTS
UPDATE tab set tab.counter = CASE WHEN (CAST 
(org.apache.derby.iapi.db.Factory::getTriggerExecutionContext().getOldRow().getObject(3)
 AS SMALLINT)  < 32767) THEN (CAST 
(org.apache.derby.iapi.db.Factory::getTriggerExecutionContext().getOldRow().getObject(3)
 AS SMALLINT)  + 1) ELSE 1 END
  WHERE ((CAST 
(org.apache.derby.iapi.db.Factory::getTriggerExecutionContext().getNewRow().getObject(3)
 AS SMALLINT)  is null) or (CAST 
(org.apache.derby.iapi.db.Factory::getTriggerExecutionContext().getOldRow().getObject(3)
 AS SMALLINT)  = CAST 
(org.apache.derby.iapi.db.Factory::getTriggerExecutionContext().getNewRow().getObject(3)
 AS SMALLINT) ))
  AND CAST 
(org.apache.derby.iapi.db.Factory::getTriggerExecutionContext().getNewRow().getObject(1)
 AS INTEGER)  = tab.element_id
  AND CAST 
(org.apache.derby.iapi.db.Factory::getTriggerExecutionContext().getNewRow().getObject(2)
 AS VARCHAR(30))  = tab.altered_id

Notice the casting to VARCHAR(30) which is what the column altered_id is 
defined at during trigger creation. Later, when we alter the length to 
VARCHAR(64), we do recognize that trigger has become invalid but we simply 
pickup the above query from SYS.SYSSTATEMENTS and recompile it which really 
doesn't help because VARCHAR(30) is not really correct anymore.

Kathey had a test case that she tried where she dropped the column and 
recreated it with longer length and the trigger seemed to work correctly for 
that case. I will debug that case to see what is different about it which makes 
it work. Hopefully, the same technique can be used for our broken case. I will 
get Kathey's test case a try and debug it to understand what is going on. Her 
test case is as follows

ALTER TABLE TAB DROP COLUMN altered_id; 
ALTER TABLE TAB ADD COLUMN altered_id VARCHAR(64); 

-- insert the data 
insert into tab (element_id, altered_id, counter, timets) VALUES (99, 
'012345678901234567890123456789001234567890',1,CURRENT_TIMESTAMP); 

update tab set timets = CURRENT_TIMESTAMP where ELEMENT_ID = 99; 


> Trigger does not recognize new size of VARCHAR column  expanded with ALTER 
> TABLE. It fails with ERROR 22001: A truncation error was encountered trying 
> to shrink VARCHAR 
> -------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: DERBY-4874
>                 URL: https://issues.apache.org/jira/browse/DERBY-4874
>             Project: Derby
>          Issue Type: Bug
>    Affects Versions: 10.2.2.1, 10.3.3.1, 10.4.2.1, 10.5.3.0, 10.6.2.1, 
> 10.7.1.0
>            Reporter: Kathey Marsden
>            Assignee: Mamta A. Satoor
>         Attachments: trigAlterColumn.sql
>
>
> Trigger created before VARCHAR column is expanded with ALTER TABLE does not 
> recognize new size and fails with:
> ERROR 22001: A truncation error was encountered trying to shrink VARCHAR 
> '012345
> 678901234567890123456789001234567890' to length 30.
> CREATE TABLE tab (
>        element_id         INTEGER NOT NULL,
>        altered_id         VARCHAR(30) NOT NULL,
>        counter            SMALLINT NOT NULL DEFAULT 0,
>        timets            TIMESTAMP NOT NULL
> );
> 0 rows inserted/updated/deleted
> ij> -- Create a trigger against the table
> CREATE TRIGGER mytrig
>  AFTER UPDATE ON tab
>  REFERENCING NEW AS newt OLD AS oldt
>  FOR EACH ROW MODE DB2SQL
>   UPDATE tab set tab.counter = CASE WHEN (oldt.counter < 32767) THEN 
> (oldt.count
> er + 1) ELSE 1 END
>   WHERE ((newt.counter is null) or (oldt.counter = newt.counter))
>   AND newt.element_id = tab.element_id
>   AND newt.altered_id = tab.altered_id;
> 0 rows inserted/updated/deleted
> ij> -- Alter the table to increase column
> ALTER TABLE tab ALTER altered_id SET DATA TYPE VARCHAR(64);
> 0 rows inserted/updated/deleted
> ij> -- insert the data
> insert into tab values (99, 
> '012345678901234567890123456789001234567890',1,CURRE
> NT_TIMESTAMP);
> 1 row inserted/updated/deleted
> ij> -- update and reproduce the issue
> update tab set timets = CURRENT_TIMESTAMP where ELEMENT_ID = 99;
> ERROR 22001: A truncation error was encountered trying to shrink VARCHAR 
> '012345
> 678901234567890123456789001234567890' to length 30.
> java.sql.SQLDataException: A truncation error was encountered trying to 
> shrink V
> ARCHAR '012345678901234567890123456789001234567890' to length 30.
>         at 
> org.apache.derby.impl.jdbc.SQLExceptionFactory40.getSQLException(SQLE
> xceptionFactory40.java:79)
>         at 
> org.apache.derby.impl.jdbc.Util.generateCsSQLException(Util.java:256)
>         at 
> org.apache.derby.impl.jdbc.TransactionResourceImpl.wrapInSQLException
> (TransactionResourceImpl.java:391)
>         at 
> org.apache.derby.impl.jdbc.TransactionResourceImpl.handleException(Tr
> ansactionResourceImpl.java:346)
>         at 
> org.apache.derby.impl.jdbc.EmbedConnection.handleException(EmbedConne
> ction.java:2269)
>         at 
> org.apache.derby.impl.jdbc.ConnectionChild.handleException(Connection
> Child.java:81)
>         at 
> org.apache.derby.impl.jdbc.EmbedStatement.executeStatement(EmbedState
> ment.java:1321)
>         at 
> org.apache.derby.impl.jdbc.EmbedStatement.execute(EmbedStatement.java
> :625)
>         at 
> org.apache.derby.impl.jdbc.EmbedStatement.execute(EmbedStatement.java
> :555)
>         at org.apache.derby.impl.tools.ij.ij.executeImmediate(ij.java:367)
>         at org.apache.derby.impl.tools.ij.utilMain.doCatch(utilMain.java:521)
>         at 
> org.apache.derby.impl.tools.ij.utilMain.runScriptGuts(utilMain.java:3
> 63)
>         at org.apache.derby.impl.tools.ij.utilMain.go(utilMain.java:261)
>         at org.apache.derby.impl.tools.ij.Main.go(Main.java:229)
>         at org.apache.derby.impl.tools.ij.Main.mainCore(Main.java:184)
>         at org.apache.derby.impl.tools.ij.Main.main(Main.java:75)
>         at org.apache.derby.tools.ij.main(ij.java:59)
> Caused by: java.sql.SQLException: A truncation error was encountered trying 
> to s
> hrink VARCHAR '012345678901234567890123456789001234567890' to length 30.
>         at 
> org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException(SQLExc
> eptionFactory.java:45)
>         at 
> org.apache.derby.impl.jdbc.SQLExceptionFactory40.wrapArgsForTransport
> AcrossDRDA(SQLExceptionFactory40.java:119)
>         at 
> org.apache.derby.impl.jdbc.SQLExceptionFactory40.getSQLException(SQLE
> xceptionFactory40.java:70)
>         ... 16 more
> Caused by: ERROR 22001: A truncation error was encountered trying to shrink 
> VARC
> HAR '012345678901234567890123456789001234567890' to length 30.
>         at 
> org.apache.derby.iapi.error.StandardException.newException(StandardEx
> ception.java:343)
>         at 
> org.apache.derby.iapi.types.SQLChar.hasNonBlankChars(SQLChar.java:176
> 6)
>         at org.apache.derby.iapi.types.SQLChar.setWidth(SQLChar.java:1840)
>         at 
> org.apache.derby.exe.ac0b5b0099x012bxf542xab11x0000001bd2983.e2(Unkno
> wn Source)
>         at 
> org.apache.derby.impl.services.reflect.DirectCall.invoke(ReflectGener
> atedClass.java:143)
>         at 
> org.apache.derby.impl.sql.execute.GenericQualifier.getOrderable(Gener
> icQualifier.java:96)
>         at 
> org.apache.derby.impl.sql.execute.NoPutResultSetImpl.clearOrderableCa
> che(NoPutResultSetImpl.java:313)
>         at 
> org.apache.derby.impl.sql.execute.TableScanResultSet.openScanControll
> er(TableScanResultSet.java:350)
>         at 
> org.apache.derby.impl.sql.execute.TableScanResultSet.openCore(TableSc
> anResultSet.java:262)
>         at 
> org.apache.derby.impl.sql.execute.ProjectRestrictResultSet.openCore(P
> rojectRestrictResultSet.java:174)
>         at 
> org.apache.derby.impl.sql.execute.ProjectRestrictResultSet.openCore(P
> rojectRestrictResultSet.java:174)
>         at 
> org.apache.derby.impl.sql.execute.NormalizeResultSet.openCore(Normali
> zeResultSet.java:146)
>         at 
> org.apache.derby.impl.sql.execute.UpdateResultSet.setup(UpdateResultS
> et.java:344)
>         at 
> org.apache.derby.impl.sql.execute.UpdateResultSet.open(UpdateResultSe
> t.java:263)
>         at 
> org.apache.derby.impl.sql.GenericPreparedStatement.executeStmt(Generi
> cPreparedStatement.java:436)
>         at 
> org.apache.derby.impl.sql.GenericPreparedStatement.executeSubStatemen
> t(GenericPreparedStatement.java:306)
>         at 
> org.apache.derby.impl.sql.execute.GenericTriggerExecutor.executeSPS(G
> enericTriggerExecutor.java:173)
>         at 
> org.apache.derby.impl.sql.execute.RowTriggerExecutor.fireTrigger(RowT
> riggerExecutor.java:111)
>         at 
> org.apache.derby.impl.sql.execute.TriggerEventActivator.notifyEvent(T
> riggerEventActivator.java:278)
>         at 
> org.apache.derby.impl.sql.execute.UpdateResultSet.fireAfterTriggers(U
> pdateResultSet.java:817)
>         at 
> org.apache.derby.impl.sql.execute.UpdateResultSet.open(UpdateResultSe
> t.java:280)
>         at 
> org.apache.derby.impl.sql.GenericPreparedStatement.executeStmt(Generi
> cPreparedStatement.java:436)
>         at 
> org.apache.derby.impl.sql.GenericPreparedStatement.execute(GenericPre
> paredStatement.java:317)
>         at 
> org.apache.derby.impl.jdbc.EmbedStatement.executeStatement(EmbedState
> ment.java:1232)
>         ... 10 more
> ij>

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