[teiid-issues] [JBoss JIRA] (TEIID-5290) NOW() function returns the same value for each call in BEGIN...END block

[Steven Hawkins (JIRA)]

    [ https://issues.jboss.org/browse/TEIID-5290?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13548437#comment-13548437 ] 

Steven Hawkins commented on TEIID-5290:
---------------------------------------

This is mostly about the function definition for now/current_timestamp - it is defined as command deterministic, which as per TEIID-5204 means that it should have a single value for the scope of the user command.

There is no difference in the behavior in this case between using "declare timestamp ts2 = now()" and "declare timestamp ts2 = (select now())" as we are still only looking for the command level value.  

getdate and clock_timestamp are the fully non-deterministic timestamp functions for sql server and postgresql respectively.  Postgresql actually offers:

transaction_timestamp() - same as pg now()
statement_timestamp()
clock_timestamp()

Our current behavior for now / current_timestamp matches pg statement_timestamp.  If you use now() in the postgresql example above, it will produce the same value for each timestamp.

It appears that SQL Server and postgresql disagree on the meaning of current_timestamp - it's fully non-deterministc for SQL Server and it matches transaction_timetstamp for postgresql.  The spec does not seem to fully specify what current means.

Our choices here are:
1. leave the Teiid current_timestamp / now functions as command deterministic as per TEIID-5204 and introduce a new fully non-deterministic timestamp function.
2. change the Teiid current_timestamp / now functions back to the non-determinisic implementation and update the metadata to indicate it is fully non-deterministic.

Do you have a preference as to the resolution?

> NOW() function returns the same value for each call in BEGIN...END block
> ------------------------------------------------------------------------
>
>                 Key: TEIID-5290
>                 URL: https://issues.jboss.org/browse/TEIID-5290
>             Project: Teiid
>          Issue Type: Bug
>          Components: Query Engine
>    Affects Versions: 10.1
>         Environment: teiid-10.1.0 on WildFly Full 11.0.0.Final (WildFly Core 3.0.8.Final)
>            Reporter: dalex dalex
>            Assignee: Steven Hawkins
>             Fix For: 10.2
>
>
> Run the following queries:
> {code:sql}
> BEGIN
> 	declare timestamp ts1 = select now();
> 	DECLARE integer c = 20000;
> 	WHILE (c > 0) 
> 		BEGIN
> 			c= c-1; 
> 		END
> 	declare timestamp ts2 = select now();
> 	select ts1, ts2;
> END ;;
> {code}
> and
> {code:sql}
> BEGIN
> 	DECLARE integer c = 20000;
> 	create local temporary table #tem(ts timestamp);
> 	WHILE (c > 0) 
> 		BEGIN
> 			INSERT INTO #tem VALUES((select NOW()));
> 			c= c-1; 
> 		END 
> 	select * from #tem;
> END ;;
> {code}
> NOW() function returns the same value for each call in BEGIN...END block and it doesn't matter if it is atomic or not.



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