PL/SQL
Tutorials - HANDLING ERRORS AND EXCEPTIONS
PLSQL handles the errors caused at the server level and publishes them using the following functions: EXCEPTION This datatype is declared in DECLARE section of the PLSQL code enables to call those as and when they are required. An internal exception is raised implicitly whenever your PL/SQL program violates an Oracle rule or exceeds a system-dependent limit. Every Oracle error has a number, but exceptions must be handled by name. So, PL/SQL predefines some common Oracle errors as exceptions. For example, PL/SQL raises the predefined exception NO_DATA_FOUND if a SELECT INTO statement returns no rows. To handle other Oracle errors, you can use the OTHERS handler. The functions SQLCODE and SQLERRM are especially useful in the OTHERS handler because they return the Oracle error code and message text. Alternatively, you can use the pragma EXCEPTION_INIT to associate exception names with Oracle error codes. Exception:
ACCESS_INTO_NULL
Your program attempts to assign values to the attributes of an uninitialized
(atomically null) object. None of the choices in the WHEN clauses of a CASE statement is selected, and there is no ELSE clause. Exception:
COLLECTION_IS_NULL
Your program attempts to apply collection methods other than EXISTS to
an uninitialized (atomically null) nested table or varray, or the program
attempts to assign values to the elements of an uninitialized nested table
or varray.
Your program attempts to open an already open cursor. A cursor must be
closed before it can be reopened. A cursor FOR loop automatically opens
the cursor to which it refers. So, your program cannot open that cursor
inside the loop. Exception:
DUP_VAL_ON_INDEX
Your program attempts to store duplicate values in a database column that
is constrained by a unique index.
Your program attempts an illegal cursor operation such as closing an unopened
cursor. In
a SQL statement, the conversion of a character string into a number fails
because the string does not represent a valid number. (In procedural statements,
VALUE_ERROR is raised.) This exception is also raised when the LIMIT-clause
expression in a bulk FETCH statement does not evaluate to a positive number. A
SELECT INTO statement returns no rows, or your program references a deleted
element in a nested table or an un-initialized element in an index-by
table. SQL aggregate functions such as AVG and SUM always return a value
or a null. So, a SELECT INTO statement that calls an aggregate function
never raises NO_DATA_FOUND. The FETCH statement is expected to return
no rows eventually, so when that happens, no exception is raised. Your
program issues a database call without being connected to Oracle. PL/SQL
has an internal problem. The
host cursor variable and PL/SQL cursor variable involved in an assignment
have incompatible return types. For example, when an open host cursor
variable is passed to a stored subprogram, the return types of the actual
and formal parameters must be compatible. PL/SQL
runs out of memory or memory has been corrupted. Your
program references a nested table or varray element using an index number
larger than the number of elements in the collection. Your
program references a nested table or varray element using an index number
(-1 for example) that is outside the legal range. The
conversion of a character string into a universal rowid fails because
the character string does not represent a valid rowid. A
time-out occurs while Oracle is waiting for a resource. A
SELECT INTO statement returns more than one row. Your program attempts to divide a number by zero. An Example of handling exception (from Oracle Docs) DECLARE |