Hashable data types
The database server uses a built-in bit-hashing function to produce
the hash value for a data type, which means that the built-in hash
function can be used only for bit-hashable data types. If your opaque
data type is not bit hashable, the database server cannot use its
built-in hash function for the equality comparison. Therefore, if
your data type is not bit-hashable, you cannot use it in the following
cases:
- In the GROUP BY clause of a SELECT statement
- In hash joins
- With the IN operator in a WHERE clause
- COUNT DISTINCT aggregates