Sql-server – How to have more than 100 entries in case statement as a variable

sql-server-2012t-sql

I wrote a case statement with > 100 choices where I am using the same statement in 4 places in a simple query.

The same query twice with a union between them but also is doing a count and therefore the group by also contains the case statement.

This is to relabel some company names where different records for the same company are spelled differently.

I tried to declare a variable as a VarChar(MAX)

declare @CaseForAccountConsolidation varchar(max)

SET @CaseForAccountConsolidation = 'CASE 
       WHEN ac.accountName like ''AIR NEW Z%'' THEN ''AIR NEW ZEALAND''
       WHEN ac.accountName LIKE ''AIR BP%'' THEN ''AIR BP''
       WHEN ac.accountName LIKE ''ADDICTION ADVICE%'' THEN ''ADDICTION ADVICE''
       WHEN ac.accountName LIKE ''AIA%'' THEN ''AIA''
       ...

When I went to use it in my select statement – the query just returned the case statement as text and didn't evaluate it.

I also was unable to use it in the group by – I got this error message:

Each GROUP BY expression must contain at least one column that is not an outer reference.

Ideally I would like to have the CASE in just a single place – so that there is no chance of me updating one line and not replicating that elsewhere.

Is there some way of doing this?

I am open to other ways (Like maybe a function – but I am not sure how to use them like this)

Here is a sample of the SELECT I am currently using

SELECT 
   SUM(c.charge_amount) AS GSTExcl
   ,dl.FirstDateOfMonth AS MonthBilled
   ,dl.FirstDateOfWeek AS WeekBilled
   ,CASE 
       WHEN ac.accountName like 'AIR NEW Z%' THEN 'AIR NEW ZEALAND'
       WHEN ac.accountName LIKE 'AIR BP%' THEN 'AIR BP'
       WHEN ac.accountName LIKE 'ADDICTION ADVICE%' THEN 'ADDICTION ADVICE'
       WHEN ac.accountName LIKE 'AIA%' THEN 'AIA'
       ELSE ac.accountName
   END AS accountName
   ,dl.FinancialYear
   ,CONVERT(Date,c.date_charged) AS date_charged
FROM [accession] a
   LEFT JOIN account_code ac ON a.account_code_id = ac.account_code_id
   LEFT Join charge c ON a.accession_id = c.accession_id
   LEFT JOIN dateLookup dl ON convert(date,c.date_charged) = dl.date
WHERE a.datecreated = CONVERT(DATE,now())
GROUP BY
   dl.FirstDateOfMonth
   ,dl.FinancialYear
   ,dl.FirstDateOfWeek
   ,CONVERT(Date,c.date_charged)
   ,CASE 
       WHEN ac.accountName like 'AIR NEW Z%' THEN 'AIR NEW ZEALAND'
       WHEN ac.accountName LIKE 'AIR BP%' THEN 'AIR BP'
       WHEN ac.accountName LIKE 'ADDICTION ADVICE%' THEN 'ADDICTION ADVICE'
       WHEN ac.accountName LIKE 'AIA%' THEN 'AIA'
       ELSE ac.accountName
   END

UNION

SELECT 
   SUM(c.charge_amount) AS GSTExcl
   ,dl.FirstDateOfMonth AS MonthBilled
   ,dl.FirstDateOfWeek AS WeekBilled
   ,CASE 
       WHEN ac.accountName like 'AIR NEW Z%' THEN 'AIR NEW ZEALAND'
       WHEN ac.accountName LIKE 'AIR BP%' THEN 'AIR BP'
       WHEN ac.accountName LIKE 'ADDICTION ADVICE%' THEN 'ADDICTION ADVICE'
       WHEN ac.accountName LIKE 'AIA%' THEN 'AIA'
       ELSE ac.accountName
   END AS accountName
   ,dl.FinancialYear
   ,CONVERT(Date,c.date_charged) AS date_charged
FROM [accession] a
   LEFT JOIN account_code ac ON a.account_code_id = ac.account_code_id
   LEFT Join charge c ON a.accession_id = c.accession_id
   LEFT JOIN dateLookup dl ON convert(date,c.date_charged) = dl.date
WHERE a.datecreated = DATEADD(YEAR,-1,CONVERT(DATE,now()))
GROUP BY
   dl.FirstDateOfMonth
   ,dl.FinancialYear
   ,dl.FirstDateOfWeek
   ,CONVERT(Date,c.date_charged)
   ,CASE 
       WHEN ac.accountName like 'AIR NEW Z%' THEN 'AIR NEW ZEALAND'
       WHEN ac.accountName LIKE 'AIR BP%' THEN 'AIR BP'
       WHEN ac.accountName LIKE 'ADDICTION ADVICE%' THEN 'ADDICTION ADVICE'
       WHEN ac.accountName LIKE 'AIA%' THEN 'AIA'
       ELSE ac.accountName
   END

The purpose for this UNION is to return all data for a timeperiod, and ALSO to return data for the same timeperiod for 12 months previously

EDIT: Added a missing "CATCH-ALL"
EDIT2: Added a second ½ of the UNION statement
EDIT3: Corrected the GROUP BY to include some other necessary elements

Best Answer

One easy way to eliminate the repetition of the CASE expression is to use CROSS APPLY like this:

SELECT 
   SUM(c.charge_amount) AS GSTExcl
   ,dl.FirstDateOfMonth AS MonthBilled
   ,dl.FirstDateOfWeek AS WeekBilled
   ,x.accountName
   ,dl.FinancialYear
   ,CONVERT(Date,c.date_charged) AS date_charged
FROM [accession] a
   LEFT JOIN account_code ac ON a.account_code_id = ac.account_code_id
   CROSS APPLY
   (
    SELECT 
       CASE 
           WHEN ac.accountName like 'AIR NEW Z%' THEN 'AIR NEW ZEALAND'
           WHEN ac.accountName LIKE 'AIR BP%' THEN 'AIR BP'
           WHEN ac.accountName LIKE 'ADDICTION ADVICE%' THEN 'ADDICTION ADVICE'
           WHEN ac.accountName LIKE 'AIA%' THEN 'AIA'
       END AS accountName
   ) AS x
   LEFT Join charge c ON a.accession_id = c.accession_id
   LEFT JOIN dateLookup dl ON convert(date,c.date_charged) = dl.date
GROUP BY
   dl.FirstDateOfMonth
   ,x.AccountName

With the help of CROSS APPLY you assign a name to your CASE expression in such a way that it can be referenced anywhere in your statement. It works because strictly speaking you are defining the computed column in a nested SELECT – the FROM-less SELECT that follows the CROSS APPLY.

This is the same as referencing an aliased column of a derived table – which technically this nested SELECT is. It is both a correlated subquery and a derived table. As a correlated subquery, it is allowed to reference the outer scope's columns, and as a derived table it allows the outer scope to reference the columns it defines.

For a UNION query that uses the same CASE expression, you have to define it in each leg, there is no workaround for that except to use a completely different replacement method instead of the CASE. However, in your specific case it is possible to fetch the results without UNION.

The two legs differ in the WHERE condition only. One has this:

WHERE a.datecreated = CONVERT(DATE,now())

and the other this:

WHERE a.datecreated = DATEADD(YEAR,-1,CONVERT(DATE,now()))

You can combine them like this:

WHERE a.datecreated IN (
                        CONVERT(DATE,now()),
                        DATEADD(YEAR,-1,CONVERT(DATE,now()))
                       )

and apply it to the modified SELECT at the beginning of this answer.

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