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Thread: Query with conditional statement

Query with conditional statement

From
JORGE MALDONADO
Date:
Hi,

Can a conditional CASE statement be part of the SELECT portion of a query? For example:

SELECT
fld1, fld2, fld3,
CASE 
    WHEN condition1 THEN fldx1 AS a1, fldx2 AS a2, fldx3 AS a3
    WHEN condition2 THEN fldy1 AS b1, fldy2 AS b2, fldy3 AS b3
    ELSE .....
END,
fld6, fld7
FROM ......
WHERE ......

I ran a test and see the following:
* Each WHEN only accepts 1 result and not 3 as shown in the example
* The AS for the alias is not supported

I need to return more than 1 field on each WHEN and also assign an ALIAS.
I very much appreciate your feedback.

Regards,
Jorge Maldonado

RE: Query with conditional statement

From
"Tchouante, Merlin"
Date:

Yes, it can.

 

Thanks,

  -- Merlin

 

 

Merlin D. Tchouante, Sr. IT Enterprise Application Developer
Center for Information Technology Services (CITS)
601 West Lombard Street
Baltimore, Maryland 21201-1512
mtchouan@umaryland.edu 
410-706-4489 * 410-706-1500 fax

 

Please send Blackboard questions to the CITS support email address:  DL-CITSBbSupport@umaryland.edu

Please send Mediasite questions to the CITS support email address:  DL-CITSMediasiteSupport@umaryland.edu

 

 

From: JORGE MALDONADO <jorgemal1960@gmail.com>
Sent: Wednesday, September 13, 2023 1:52 PM
To: pgsql-sql@postgresql.org
Subject: Query with conditional statement

 

CAUTION: This message originated from a non-UMB email system. Hover over any links before clicking and use caution opening attachments.

Hi,

 

Can a conditional CASE statement be part of the SELECT portion of a query? For example:

 

SELECT

fld1, fld2, fld3,

CASE 

    WHEN condition1 THEN fldx1 AS a1, fldx2 AS a2, fldx3 AS a3

    WHEN condition2 THEN fldy1 AS b1, fldy2 AS b2, fldy3 AS b3

    ELSE .....

END,

fld6, fld7

FROM ......

WHERE ......

 

I ran a test and see the following:

* Each WHEN only accepts 1 result and not 3 as shown in the example

* The AS for the alias is not supported

 

I need to return more than 1 field on each WHEN and also assign an ALIAS.

I very much appreciate your feedback.

 

Regards,

Jorge Maldonado

Attachment

Re: Query with conditional statement

From
"David G. Johnston"
Date:
On Wed, Sep 13, 2023 at 10:53 AM JORGE MALDONADO <jorgemal1960@gmail.com> wrote:
I need to return more than 1 field on each WHEN and also assign an ALIAS.


You can only produce a single value of a specific data type from the output of a case expression.   To do what you desire, create a custom composite type and return that.  You get to name the fields when you define the composite type.

David J.

Re: Query with conditional statement

From
Mehmet Sabri KUNT
Date:
Hi Jorge,
You can not use the case statement like in your code.

If you want to get a different field's value by your condition you can use the case statement like the following examples.


select 
id,
CASE WHEN condition1 THEN fldx1 END AS a1,
CASE WHEN condition1 THEN fldx2 END AS a2,
CASE WHEN condition1 THEN fldx3 END AS a3,
CASE WHEN condition2 THEN fldy1 END AS b1,
CASE WHEN condition2 THEN fldy2 END AS b2,
CASE WHEN condition2 THEN fldy3 END AS b3
FROM your_table

If you use like above, you have lots of null values.  

If you don't have to use column names like a1, a2,a3, b1,b2, or b3 like in your code, I suggest using like the following

select
id,
CASE 
        WHEN condition1 THEN fldx1 
        WHEN condition2 THEN fldy1 
        ELSE aaa1
END AS a1,
CASE 
        WHEN condition1 THEN fldx2 
        WHEN condition2 THEN fldy2 
        ELSE aaa2
END AS a2,
CASE 
        WHEN condition1 THEN fldx3 
        WHEN condition2 THEN fldy3
        ELSE aaa3
END AS a3
FROM your_table

Shane Borden <sborden76@gmail.com>, 14 Eyl 2023 Per, 01:43 tarihinde şunu yazdı:
You will need to do a CASE statement for each column.  I’m not aware of being able to return multiple columns from one case. 

Shane Borden
sborden76@gmail.com
Sent from my iPhone

On Sep 13, 2023, at 4:23 PM, Tchouante, Merlin <mtchouan@umaryland.edu> wrote:



Yes, it can.

 

Thanks,

  -- Merlin

 

 

Merlin D. Tchouante, Sr. IT Enterprise Application Developer
Center for Information Technology Services (CITS)
601 West Lombard Street
Baltimore, Maryland 21201-1512
mtchouan@umaryland.edu 
410-706-4489 * 410-706-1500 fax

 

Please send Blackboard questions to the CITS support email address:  DL-CITSBbSupport@umaryland.edu

Please send Mediasite questions to the CITS support email address:  DL-CITSMediasiteSupport@umaryland.edu

 

<image001.png>

 

From: JORGE MALDONADO <jorgemal1960@gmail.com>
Sent: Wednesday, September 13, 2023 1:52 PM
To: pgsql-sql@postgresql.org
Subject: Query with conditional statement

 

CAUTION: This message originated from a non-UMB email system. Hover over any links before clicking and use caution opening attachments.

Hi,

 

Can a conditional CASE statement be part of the SELECT portion of a query? For example:

 

SELECT

fld1, fld2, fld3,

CASE 

    WHEN condition1 THEN fldx1 AS a1, fldx2 AS a2, fldx3 AS a3

    WHEN condition2 THEN fldy1 AS b1, fldy2 AS b2, fldy3 AS b3

    ELSE .....

END,

fld6, fld7

FROM ......

WHERE ......

 

I ran a test and see the following:

* Each WHEN only accepts 1 result and not 3 as shown in the example

* The AS for the alias is not supported

 

I need to return more than 1 field on each WHEN and also assign an ALIAS.

I very much appreciate your feedback.

 

Regards,

Jorge Maldonado