Case statement in PostgreSQL

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In PostgreSQL, or even in SQL in general, a case statement can be used to create an inline conditional statement. For example,

select SUM(amount) total_amount,
SUM(CASE WHEN type IN ('penalties', 'deductions') THEN amount ELSE 0 END) as total_credit_amount,
from transactions

In the example above, the total_amount applies for all types; however, total_credit_amount only applies if the record type is ‘penalties’ or ‘deductions’.