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From Rainer Döbele (JIRA) <empire-db-...@incubator.apache.org>
Subject [jira] Commented: (EMPIREDB-75) DBCommand should allow me to select duplicate columns
Date Thu, 01 Apr 2010 08:39:27 GMT

    [ https://issues.apache.org/jira/browse/EMPIREDB-75?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12852289#action_12852289
] 

Rainer Döbele commented on EMPIREDB-75:
---------------------------------------

Hi Greg

The reason why we're not allowing to select the same column twice is that we need to address
this column in a result set (reader) or a record, hence if the same column expression is selected
twice we don't know which column to address.

However it is still possible to select the same column twice - all you need to do is to rename
one of them like this:
cmd.select(T.C1, T.C1.as("C2"));
In this case we'll have two different objects and are now able to address the individual columns.

Hence it don't think it is necessary to create an overload for column selection in the DBCommand
as you suggested.
Do you mind if I close this issue als "not a Problem"?


> DBCommand should allow me to select duplicate columns
> -----------------------------------------------------
>
>                 Key: EMPIREDB-75
>                 URL: https://issues.apache.org/jira/browse/EMPIREDB-75
>             Project: Empire-DB
>          Issue Type: Bug
>          Components: Core
>    Affects Versions: empire-db-2.0.5-incubating
>         Environment: Win32, JDK1.6.0_15
>            Reporter: Greg Reiser
>
> Allowing the option to (explicitly) select a duplicate column in DBCommand would be helpful
for a UNION type of statement. Here is the scenario: I have enterprise educators that are
able to work within all colleges in a university while I have others that can only work in
specific colleges (specialized). Also, each educator can have an enterprise id and/or a facility-specific
ID. I need to be able to query the possible educators for a specific college. Here is my SQL:
> SELECT t70.EDUCATOR_CODE, t69.EDUCATOR_ID, t69.EDUCATOR_SID
> FROM EDUCATOR t69, EDUCATOR_FACILITY t70
> WHERE t69.EDUCATOR_SID=t70.EDUCATOR_SID AND t69.STATUS=1 AND t70.FACILITY_SID=355 
> UNION 
> SELECT t69.EDUCATOR_ID, t69.EDUCATOR_ID, t69.EDUCATOR_SID
> FROM EDUCATOR t69
> WHERE t69.FACILITY_MAP_CODE=1 AND t69.STATUS=1
> An overloaded select() method on DBCommand was sufficient in my dev environment:
> public void select(DBColumnExpr expr, boolean allowDuplicateColumns)
>     { // Select this column
>         if (select == null)
>             select = new ArrayList<DBColumnExpr>();
>         if (expr != null && allowDuplicateColumns ? true : (select.contains(expr)
== false))
>             select.add(expr);
>     }

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