SQL check if table exist and truncate

问题

I'm trying to code a statement that checks if a table exist and if it does to truncate/delete it. If it doesn't exist, to print the message 'This table does not exist!'

This is what I've come up so far but doesn't seem to work.

BEGIN
         TRUNCATE TABLE PPA_P6_2018;
    EXCEPTION
        WHEN OTHERS THEN
            IF SQLCODE = -942 THEN
                DBMS_OUTPUT.put_line('This table does not exist!');
            ELSE
                RAISE;
                DBMS_OUTPUT.put_line('This table has been delted!');
            END IF;
    END;

回答1:

DECLARE
    v_count        NUMBER;
    v_table_name   VARCHAR2 (100) := 'YOURTABLE';
    v_sqlstr       VARCHAR2 (1000);
BEGIN
    SELECT   COUNT ( * )
      INTO   v_count
      FROM   user_tables
     WHERE   table_name = v_table_name;

    IF v_count > 0
    THEN
        v_sqlstr := 'DELETE FROM ' || v_table_name;

        EXECUTE IMMEDIATE v_sqlstr;

        DBMS_OUTPUT.put_line (
            'TABLE ' || v_table_name || ' HAS BEEN DELETED!');
    ELSE
        DBMS_OUTPUT.put_line ('TABLE ' || v_table_name || ' DOES NOT EXIST!');
    END IF;
END;

回答2:

Create a custom exception to catch when the table does not exist and then only catch that single exception (rather than catching all of them with OTHERS) and then use EXECUTE IMMEDIATE to truncate/drop the table:

DECLARE
  table_name VARCHAR2(30) := 'PPA_P6_2018';
  table_not_exists EXCEPTION;
  PRAGMA EXCEPTION_INIT( table_not_exists, -942 );
BEGIN
  EXECUTE IMMEDIATE 'TRUNCATE TABLE ' || table_name;
  EXECUTE IMMEDIATE 'DROP TABLE ' || table_name;
  DBMS_OUTPUT.put_line('This table has been deleted!');
EXCEPTION
  WHEN table_not_exists THEN
    DBMS_OUTPUT.put_line('This table does not exist!');
END;
/

db<>fiddle

回答3:

TRUNCATE TABLE is DDL so cannot be run directly within PL/SQL. You need to use EXECUTE IMMEDIATE:

BEGIN
    EXECUTE IMMEDIATE 'TRUNCATE TABLE PPA_P6_2018';
EXCEPTION
    WHEN OTHERS THEN
        IF SQLCODE = -942 THEN
            DBMS_OUTPUT.put_line('This table does not exist!');
        ELSE
            RAISE;
            DBMS_OUTPUT.put_line('This table has been delted!');
        END IF;
END;

Note: You will never see the message 'This table has been delted!' since the RAISE before it throws you out of the block! And if you got an error, the table hasn't been deleted anyway!

来源：https://stackoverflow.com/questions/58658067/sql-check-if-table-exist-and-truncate

标签

sql

Oracle

plsql