SQL query question

I need to write a SQL query on SQL Server 2008 to make a summary report, which consists of [Company, Type, Amount].  
but there are multiple columns for amount, and depending on Company and Type, I need to select different columns to get the amount.

For a simplified example, my source data looks like this:

Data(Bank, TranType, Col1, Col2, Col3)

'ANZ', 'A', 1000, 1005, 980
'ANZ', 'B', 500, 502, 496
'ANZ', 'C', 1000, 1000, 1000
'HSBC', 'A', 1000, 1005, 980
'HSBC', 'B', 500, 502, 496
'CITI', 'C', 1000, 1000, 1000

And I have a table like this for rules:

Rule(Bank, TranType, Field)

'ANZ', 'A', 'Col1'
'ANZ', 'B', 'Col2'
'ANZ', 'C', 'Col3'
'HSBC', 'A', 'Col2'
'HSBC', 'B', 'Col3'
'CITI', 'A', 'Col1'

Any simple query to solve this ? Experts, your help is really appreciated...
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Habib PourfardSoftware DeveloperCommented:
You can use Case When like the following code:

SELECT Bank, TranType,
	CASE WHEN Bank = 'ANZ' THEN Col1 
	WHEN Bank = 'BNZ' OR Bank = 'HSBC' Then Col2
FROM data
GROUP BY Bank, TranType

Open in new window

TakamasaAuthor Commented:
Hi Habib,
Thank you for your suggestion.

The rule table actually is a very long list and it can change quite often, so I do not want to hard-code the rule...
Habib PourfardSoftware DeveloperCommented:
You could create a View and use it as a source for different reports, I don't have any other idea.
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You show trantype of 'C' for bank CITI in data and trantype of 'A' for bank CITI in rule. Is that a typo? Also, can you post what your desired output should be given this sample data?
TakamasaAuthor Commented:
Hi awking00

Thank you for your reply.
If the combinaton of Bank-TranType do not match, then the report will not pick up.
The output would look like this:

ANZ, A, 1000
ANZ, B, 502
ANZ, C, 1000
HSBC, A, 1005
HSBC, B, 496
TakamasaAuthor Commented:
Hi Habib,

Thank you for your suggestion.

Below query returns the output I am looking for, but in my real case the CASE statement would get very long (40+ when clauses). I was hoping there might be a smarter way than that but maybe some hard-coding cannot be avoided...

		when b.colname = 'col1' then a.col1
		when b.colname = 'col2' then a.col2
		when b.colname = 'col3' then a.col3
	end as amount
	data a
	inner join 
	rule b
	a.bank = b.bank 
	and a.trantype = b.trantype

Open in new window

Vikas GargBusiness Intelligence DeveloperCommented:

You can try the following code which will meet your requirements

select *
from Bank a
  for BankRulecol in ([Col1],[Col2],[Col3])
) unpiv
) TB
INNER JOIN BankRule B ON TB.Bank = B.Bank AND TB.TranType = B.TranType AND TB.BankRulecol = LTRIM(B.Field)

Open in new window


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What dbms (version and release) are you using (e.g. Oracle 11gR2)?
TakamasaAuthor Commented:
Hello Vikas

This is great. Thank you for your help !
TakamasaAuthor Commented:
Hi awking00

I am using SQL Server 2008 R2.
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