exception usage in oracle

EXCEPTION is used to handle exceptions in SQL or PL/SQL by executing handling code for specific exception types through the EXCEPTION block. Oracle provides predefined exception types (such as NO_DATA_FOUND, TOO_MANY_ROWS), which can handle different exception types as needed. Best practices recommend always handling exceptions explicitly and providing clear error messages.

EXCEPTION Usage in Oracle

The EXCEPTION keyword is used to process SQL statements or PL/SQL blocks that may An abnormal situation occurred.

Syntax

BEGIN
  -- SQL 代码或 PL/SQL 块
EXCEPTION
  -- 异常处理代码
END;

Exception type

Oracle provides predefined exception types, such as:

• NO_DATA_FOUND: Data not found
• TOO_MANY_ROWS: More rows returned than expected
• INVALID_CURSOR: Invalid The cursor
• NOT_SUPPORTED: The operation does not support

Exception handling

When an exception occurs, the exception handling code will be executed. There can be multiple EXCEPTION blocks to handle different exception types.

Example

The following example demonstrates how to use EXCEPTION to handle the NO_DATA_FOUND exception:

BEGIN
  SELECT * FROM employees WHERE id = 10;
EXCEPTION
  WHEN NO_DATA_FOUND THEN
    DBMS_OUTPUT.PUT_LINE('No employee with ID 10 was found.');
END;

Additional features

• WHEN OTHERS: Handles all exceptions of unspecified type.
• RAISE_APPLICATION_ERROR: Raise a custom exception.
• pragma EXCEPTION_INIT: Specifies the initial value of the exception handler.

Best Practices

• Always handle exceptions that may occur.
• Use explicit exception handling instead of relying on default behavior.
• Provide clear and user-friendly error messages.
• Use the WHEN OTHERS statement as a last resort to catch all unhandled exceptions.

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