How to chose Table based on parameterized database name? - sql

Question

My code takes in a parameter ${ID}$ (string) and based on what ID evaluates to I want to chose a different table to use. Guess I cant use a case inside a FROM statement. Some example code looks like:
select *
from ${ID}$_charges.transaction_charge
where execution_date = '2011-03-22'
So if ID is 'N' then I want to use the transaction_charge table so the statement resolves to N_charges.transaction_charge
However if ID is 'B' or 'P' then I want to use a different table called conformity_charge and the statement would evaluate to B_charges.conformity_charge or P_charges.conformity_charge
How can I write this statement?

Answer 1

If you have a low number of possible tables to target, the closest you can get, apart from dynamic SQL, is:
NOTE: Depending of the capabilities of your database engine and the size of your tables there might be performance penalties that may or may not matter.
SELECT a, b, c
FROM (
SELECT 'N' as TableName, a, b, c
FROM N_charges.transaction_charge
UNION ALL
SELECT 'P' as TableName, a, b, c
FROM P_charges.transaction_charge
UNION ALL
SELECT 'B' as TableName, a, b, c
FROM B_charges.transaction_charge
) t
WHERE TableName = '${ID}$'
# Another variation
SELECT a, b, c
FROM N_charges.transaction_charge
WHERE 'N' = '${ID}$'
UNION ALL
SELECT a, b, c
FROM P_charges.transaction_charge
WHERE 'P' = '${ID}$'
UNION ALL
SELECT a, b, c
FROM B_charges.transaction_charge
WHERE 'B' = '${ID}$'