(Oracle SQL) Catching a unique constraint error

问题

This is my code:

Declare
  violation_of_constraint EXCEPTION;
BEGIN
  -- (A FEW INSERTS HERE: A, B, C)
  SAVEPOINT X;
  -- (ANOTHER INSERT HERE: D)
  IF DUP_VAL_ON_INDEX THEN
    ROLLBACK TO X;
    COMMIT;
    RAISE violation_of_constraint;
  END IF;
EXCEPTION
  WHEN violation_of_constraint THEN
    DBMS_OUTPUT.PUT_LINE('Value already exists');
    COMMIT;
END;
/

When I run it (from the sql command line) I get this error at line 11:

expression is of wrong type (line 11 is "IF DUP_VAL_ON_INDEX THEN")

What could it be wrong?

回答1:

You need to define a nested PL/SQL Block, and handle exception in EXCEPTION BLOCK as WHEN DUP_VAL_ON_INDEX...

It should NOT be IF DUP_VAL_ON_INDEX

Declare
violation_of_constraint EXCEPTION;
BEGIN
  BEGIN
  -- (A FEW INSERTS HERE: A, B, C)
  SAVEPOINT X;
  -- (ANOTHER INSERT HERE: D)
  EXCEPTION 
  WHEN DUP_VAL_ON_INDEX THEN
    ROLLBACK TO X;
    COMMIT;
    RAISE violation_of_constraint;
  END;
EXCEPTION
WHEN violation_of_constraint THEN
DBMS_OUTPUT.PUT_LINE('Value already exists');
COMMIT;
END;
/

来源：https://stackoverflow.com/questions/22175894/oracle-sql-catching-a-unique-constraint-error