PostgreSQL

Procedures are defined with the CREATE PROCEDURE command, not CREATE FUNCTION.

Procedures do not return a function value; hence CREATE PROCEDURE lacks a RETURNS clause. However, procedures can instead return data to their callers via output parameters.

While a function is called as part of a query or DML command, a procedure is called in isolation using the CALL command.

A procedure can commit or roll back transactions during its execution (then automatically beginning a new transaction), so long as the invoking CALL command is not part of an explicit transaction block. A function cannot do that.

Certain function attributes, such as strictness, don’t apply to procedures. Those attributes control how the function is used in a query, which isn’t relevant to procedures.