Filter result using alias - sql

Question

I have a query like this
SELECT
Type = TXL.Descript, Jurisdiction = CASE WHEN TX.State = 'KD' THEN 'FD'
WHEN TX.County > '' AND TX.County IS NOT NULL THEN 'Local' ELSE 'Country' END,
State = CASE WHEN TX.State = 'FD' OR (TX.County > '' AND TX.County IS NOT NULL) THEN '' ELSE (select top 1 istIntlStateDesc from IntStateM ISM where ISM.istIntlStateCode = TX.MtcState) END,
Local = CASE WHEN TX.County > '' AND TX.County IS NOT NULL THEN TX.MtcCounty ELSE '' END,
TaxCode = TX.TaxCode, TaxDescription = TX.TaxCodeDesc, EffectiveDate = ET.EtxEffectiveDate,
Taxable = ''
FROM
ETaX ET WITH (NOLOCK)
INNER JOIN TxCast TX on ET.Code = TX.TaxCode
INNER JOIN TxLMast TXL on TXL.TCode = TX.Tax
WHERE
ET.TDate <= GETDATE()
AND ET.SDate > GETDATE()
In the UI I have a table and I want to filer each column by passing the column name and what my code is doing is adding an AND condition to the WHERE clause while filtering but if I am passing the alias name (Ex. Jurisdiction) I am getting an error like - Invalid column name 'Jurisdiction', I also can't pass the actual column name as I am using case statement in the query, for example alias Jurisdiction value is coming by combing 2 column name so, is there any way it will work even passing the alias name or any better way to do it like dynamic SQL or any other workaround?

Answer 1

If I understand correctly, you want to filter by your "aliased" fields. To do so, you have 2 options:
Use subquery writing a SELECT FROM your entire query and then filtering by Jurisdiction:
SELECT * FROM
(SELECT
Type = TXL.Descript, Jurisdiction = CASE WHEN TX.State = 'KD' THEN 'FD'
WHEN TX.County > '' AND TX.County IS NOT NULL THEN 'Local' ELSE 'Country' END,
State = CASE WHEN TX.State = 'FD' OR (TX.County > '' AND TX.County IS NOT NULL) THEN '' ELSE (select top 1 istIntlStateDesc from IntStateM ISM where ISM.istIntlStateCode = TX.MtcState) END,
Local = CASE WHEN TX.County > '' AND TX.County IS NOT NULL THEN TX.MtcCounty ELSE '' END,
TaxCode = TX.TaxCode, TaxDescription = TX.TaxCodeDesc, EffectiveDate = ET.EtxEffectiveDate,
Taxable = ''
FROM
ETaX ET WITH (NOLOCK)
INNER JOIN TxCast TX on ET.Code = TX.TaxCode
INNER JOIN TxLMast TXL on TXL.TCode = TX.Tax
WHERE
ET.TDate <= GETDATE()
AND ET.SDate > GETDATE()) AS AUX_QUERY
WHERE
Jurisdiction = -your condition here-
(Note now Jurisdiction is a result field from AUX_QUERY)
Repeat the full CASE WHEN TX.State = 'KD' THEN 'FD' WHEN TX.County > '' AND TX.County IS NOT NULL THEN 'Local' ELSE 'Country' END that you called Jurisdiction in the WHERE clause (or wherever you want to use those calculated fields:
SELECT
Type = TXL.Descript, Jurisdiction = CASE WHEN TX.State = 'KD' THEN 'FD'
WHEN TX.County > '' AND TX.County IS NOT NULL THEN 'Local' ELSE 'Country' END,
State = CASE WHEN TX.State = 'FD' OR (TX.County > '' AND TX.County IS NOT NULL) THEN '' ELSE (select top 1 istIntlStateDesc from IntStateM ISM where ISM.istIntlStateCode = TX.MtcState) END,
Local = CASE WHEN TX.County > '' AND TX.County IS NOT NULL THEN TX.MtcCounty ELSE '' END,
TaxCode = TX.TaxCode, TaxDescription = TX.TaxCodeDesc, EffectiveDate = ET.EtxEffectiveDate,
Taxable = ''
FROM
ETaX ET WITH (NOLOCK)
INNER JOIN TxCast TX on ET.Code = TX.TaxCode
INNER JOIN TxLMast TXL on TXL.TCode = TX.Tax
WHERE
ET.TDate <= GETDATE()
AND ET.SDate > GETDATE()) AS AUX_QUERY
AND
CASE WHEN TX.State = 'KD' THEN 'FD'
WHEN TX.County > '' AND TX.County IS NOT NULL THEN 'Local' ELSE 'Country' END = -your condition here-

Answer 2

Aliases cannot be used like that, look at this example
declare #table1 table (id int, text1 varchar(50), text2 varchar(50))
insert into #table1 values (1, 'one', 'two')
select t1.id,
fullname = t1.text1 + ' ' + t1.text2
from #table1 t1
where fullname = 'one two'
This will throw this exception
Invalid column name 'fullname'
The most simple solution (imho) is this
select t.id,
t.fullname
from ( select t1.id,
fullname = t1.text1 + ' ' + t1.text2
from #table1 t1
) t
where t.fullname = 'one two'
This allows the database to fully evaluate the aliased columns, and therefore it will known them so you can use the aliased columns just like other columns