[jira] [Commented] (DERBY-6358) WHERE clause should be evaluated after the joins in the FROM clause

["Mike Matrigali (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DERBY-6358?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13906101#comment-13906101 ] 

Mike Matrigali commented on DERBY-6358:
---------------------------------------

Here is the 10.2 top of branch result from running script in JIRA description:
ij version 10.2
CONNECTION0* -  jdbc:derby:wombat
* = current connection
ij> create table t1( a varchar( 10 ) );
0 rows inserted/updated/deleted
ij> create table t2( a varchar( 10 ) );
0 rows inserted/updated/deleted
ij> insert into t1( a ) values ( 'horse' ), ( 'apple' ), ( 'star' ), ( '6' );
4 rows inserted/updated/deleted
ij> insert into t2( a ) values ( '6' );
1 row inserted/updated/deleted
ij> -- ok if the cast is performed in the select list
select cast( t1.a as int )
from t1 inner join t2 on t1.a = t2.a;
1
-----------
6

1 row selected
ij> -- should succeed.
-- but we see a casting error because the WHERE clause is evaluated before the ON clause
select *
from t1 inner join t2 on t1.a = t2.a
where cast( t1.a as int ) > 5;
ERROR 22018: Invalid character string format for type INTEGER.


> WHERE clause should be evaluated after the joins in the FROM clause
> -------------------------------------------------------------------
>
>                 Key: DERBY-6358
>                 URL: https://issues.apache.org/jira/browse/DERBY-6358
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 10.11.0.0
>            Reporter: Rick Hillegas
>
> The WHERE clause is supposed to be evaluated after the inner and outer joins specified in the FROM clause. See part 2 of the SQL Standard, section 7.4 (<table expression>), general rule 1. However, it appears that Derby flattens the inner joins into a cartesian product and mixes their ON clauses into the WHERE clause. As a result, WHERE clause fragments can be evaluated before the ON clauses. The following script shows this problem:
> connect 'jdbc:derby:memory:db;create=true';
> create table t1( a varchar( 10 ) );
> create table t2( a varchar( 10 ) );
> insert into t1( a ) values ( 'horse' ), ( 'apple' ), ( 'star' ), ( '6' );
> insert into t2( a ) values ( '6' );
> -- ok if the cast is performed in the select list
> select cast( t1.a as int )
> from t1 inner join t2 on t1.a = t2.a;
> -- should succeed.
> -- but we see a casting error because the WHERE clause is evaluated before the ON clause
> select *
> from t1 inner join t2 on t1.a = t2.a
> where cast( t1.a as int ) > 5;
> Fixing this bug may result in serious performance degradation for many queries. A release note will be needed to tell users how to re-write their queries in order to get the old performance. For instance, the user may need to flatten the inner joins themselves, rewriting the query as a cartesian product with a WHERE clause.



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