Oracle中判斷表是否存在再刪除表避免報錯與MySql和SqlServer的不同

發布時間: 2012/9/11 17:20:25

不同數據庫中drop a table if it exists的不同：

In MySQL it is pretty easy to drop a table if it exists already. In Oracle and Microsoft’s SQL Server it is a little more complicated. Today I want to present you the solutions for these two DBMS’.-

MySQL:

DROP TABLE IF EXISTS [table_name]

Oracle:

BEGIN

EXECUTE IMMEDIATE 'DROP TABLE [table_name]';

EXCEPTION WHEN OTHERS THEN NULL;

END;

SQL Server:

IF EXISTS (

SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES

WHERE TABLE_NAME = '[table_name]')

DROP TABLE [table_name]

Oracle中先判斷表是否存在再新建表一例：

declare
v_exists number;
begin
       --1、任務類型 TASK_TYPE_CD 建表...
    select count(*) into v_exists from user_tables where table_name = 'EDW_T99_TASK_TYPE_CD';
    if v_exists > 0 then
    execute immediate 'drop table EDW_T99_TASK_TYPE_CD';
    end if;
    execute immediate '
    create table EDW_T99_TASK_TYPE_CD
    (
      CODE_CD   VARCHAR2(20) PRIMARY KEY,
      CODE_DESC VARCHAR2(100)
    )';
    execute immediate 'comment on table EDW_T99_TASK_TYPE_CD is ''任務類型''';
    execute immediate 'comment on column EDW_T99_TASK_TYPE_CD.CODE_CD is ''代碼''';
    execute immediate 'comment on column EDW_T99_TASK_TYPE_CD.CODE_DESC is ''代碼描述''';

       --2、買入產品代碼 BUY_TYPE_CD 建表...
    select count(*) into v_exists from user_tables where table_name = 'EDW_T99_BUY_TYPE_CD';
    if v_exists > 0 then
    execute immediate 'drop table EDW_T99_BUY_TYPE_CD';
    end if;
    execute immediate '
    create table EDW_T99_BUY_TYPE_CD
    (
      CODE_CD   VARCHAR2(20) PRIMARY KEY,
      CODE_DESC VARCHAR2(100)
    )';
    execute immediate 'comment on table EDW_T99_BUY_TYPE_CD is ''買入產品代碼''';
    execute immediate 'comment on column EDW_T99_BUY_TYPE_CD.CODE_CD is ''代碼''';
    execute immediate 'comment on column EDW_T99_BUY_TYPE_CD.CODE_DESC is ''代碼描述''';

end;
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此例用在數據倉庫項目的建T99代碼表腳本方案上；此腳本在方案中用Perl根據Excel生成。