sql server - SQL query diversification -


how can diversify sql query in following manner:

if condition_a select * x
if condition b select * b x

it seems trivial operation, cannot find or figure out solution.

you can use if condition 

if condition_a  begin  select * x  end if condition_b begin  select * b x end

if there can 1 condition satisfied out of two, change second if else statement


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