Searching an SQL Server database with Substring - tsql

Question

I have a query that extracts only two columns and trims one of the columns to only the media name. This is the query for that:
Select
[Object],
CASE WHEN MsgID = '61' THEN SUBSTRING(Parms,35,6) END AS [MEDIA]
from JnlDataSection
The results from this is:
Object
---------
061 STATEMENTS
MEDIA
---------
X01180
X01181
As you can see there are multiple medias for one object. What I want is a manual query in which I can just modify it with the object name and search one object with all of its respective medias and vice versa.
This is the query I came up with:
Select
[Object],
CASE WHEN MsgID = '61' THEN SUBSTRING(Parms,35,6) END AS [MEDIA]
WHERE [OBJECT] = '061 STATEMENTS'
from JnlDataSection
However I am receiving this error:
Msg 156, Level 15, State 1, Line 5
Incorrect syntax near the keyword 'from'.
Please Note: I'm using SQL Server Management Studio 2008.
UPDATE
After reading comments, I tried this query:
Select
[Object],
CASE WHEN MsgID = '61' THEN SUBSTRING(Parms,35,6) END AS [MEDIA]
from JnlDataSection
WHERE [MEDIA] = 'X05219'
It gave me this error:
Msg 207, Level 16, State 1, Line 5
Invalid column name 'MEDIA'.
How can I fix it?

Answer 1

To expand on #JNK's suggestion, if you want to compare against the calculated MEDIA column, here are your options:
Reproduce the CASE expression in the WHERE clause:
SELECT
[Object],
CASE WHEN MsgID = '61' THEN SUBSTRING(Parms, 35, 6) END AS [MEDIA]
FROM JnlDataSection
WHERE CASE WHEN MsgID = '61' THEN SUBSTRING(Parms, 35, 6) END = 'X05219'
;
Redefine the query as a common table expression:
WITH JnlDataSectionMedia AS (
SELECT
[Object],
CASE WHEN MsgID = '61' THEN SUBSTRING(Parms, 35, 6) END AS [MEDIA]
FROM JnlDataSection
)
SELECT *
FROM JnlDataSectionMedia
WHERE [MEDIA] = 'X05219'
;
or a (normal) subselect:
SELECT *
FROM (
SELECT
[Object],
CASE WHEN MsgID = '61' THEN SUBSTRING(Parms, 35, 6) END AS [MEDIA]
FROM JnlDataSection
) AS s
WHERE [MEDIA] = 'X05219'
;
Use CROSS APPLY:
SELECT
j.[Object],
x.[MEDIA]
FROM JnlDataSection AS j
CROSS APPLY (
SELECT CASE WHEN MsgID = '61' THEN SUBSTRING(Parms, 35, 6) END
) AS x ([MEDIA])
WHERE x.[MEDIA] = 'X05219'
;
You can also define your query as a view:
CREATE VIEW JnlDataSectionMedia
AS
SELECT
[Object],
CASE WHEN MsgID = '61' THEN SUBSTRING(Parms, 35, 6) END AS [MEDIA]
FROM JnlDataSection
;
After that, you can call it at any time like this:
SELECT [Object], [MEDIA]
FROM JnlDataSectionMedia
;
You can filter on either of the columns too, when necessary:
SELECT [Object], [MEDIA]
FROM JnlDataSectionMedia
WHERE [MEDIA] = 'X05219'
;