Oracle:如果表存在

我正在为Oracle数据库写一些迁移脚本，并希望Oracle有类似于MySQL的IF EXISTS构造的东西。

具体来说，每当我想在MySQL中删除一个表时，我就会做这样的事情

DROP TABLE IF EXISTS `table_name`;

这样，如果表不存在，DROP也不会产生错误，脚本可以继续。

Oracle有类似的机制吗?我意识到我可以使用下面的查询来检查表是否存在

SELECT * FROM dba_tables where table_name = 'table_name';

但是把它和DROP绑定在一起的语法让我很困惑。

当前回答

最好和最有效的方法是捕获“table not found”异常:这避免了检查表是否存在两次的开销;并且不会遇到DROP因为其他原因(可能很重要)失败时仍然会向调用者抛出异常的问题:

BEGIN
   EXECUTE IMMEDIATE 'DROP TABLE ' || table_name;
EXCEPTION
   WHEN OTHERS THEN
      IF SQLCODE != -942 THEN
         RAISE;
      END IF;
END;

齿顶高作为参考，下面是其他对象类型的等效块:

序列

BEGIN
  EXECUTE IMMEDIATE 'DROP SEQUENCE ' || sequence_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -2289 THEN
      RAISE;
    END IF;
END;

View

BEGIN
  EXECUTE IMMEDIATE 'DROP VIEW ' || view_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -942 THEN
      RAISE;
    END IF;
END;

触发

BEGIN
  EXECUTE IMMEDIATE 'DROP TRIGGER ' || trigger_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -4080 THEN
      RAISE;
    END IF;
END;

指数

BEGIN
  EXECUTE IMMEDIATE 'DROP INDEX ' || index_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -1418 THEN
      RAISE;
    END IF;
END;

列

BEGIN
  EXECUTE IMMEDIATE 'ALTER TABLE ' || table_name
                || ' DROP COLUMN ' || column_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -904 AND SQLCODE != -942 THEN
      RAISE;
    END IF;
END;

数据库链接

BEGIN
  EXECUTE IMMEDIATE 'DROP DATABASE LINK ' || dblink_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -2024 THEN
      RAISE;
    END IF;
END;

物化视图

BEGIN
  EXECUTE IMMEDIATE 'DROP MATERIALIZED VIEW ' || mview_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -12003 THEN
      RAISE;
    END IF;
END;

Type

BEGIN
  EXECUTE IMMEDIATE 'DROP TYPE ' || type_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -4043 THEN
      RAISE;
    END IF;
END;

约束

BEGIN
  EXECUTE IMMEDIATE 'ALTER TABLE ' || table_name
            || ' DROP CONSTRAINT ' || constraint_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -2443 AND SQLCODE != -942 THEN
      RAISE;
    END IF;
END;

调度程序工作

BEGIN
  DBMS_SCHEDULER.drop_job(job_name);
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -27475 THEN
      RAISE;
    END IF;
END;

用户/架构

BEGIN
  EXECUTE IMMEDIATE 'DROP USER ' || user_name;
  /* you may or may not want to add CASCADE */
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -1918 THEN
      RAISE;
    END IF;
END;

包

BEGIN
  EXECUTE IMMEDIATE 'DROP PACKAGE ' || package_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -4043 THEN
      RAISE;
    END IF;
END;

过程

BEGIN
  EXECUTE IMMEDIATE 'DROP PROCEDURE ' || procedure_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -4043 THEN
      RAISE;
    END IF;
END;

函数

BEGIN
  EXECUTE IMMEDIATE 'DROP FUNCTION ' || function_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -4043 THEN
      RAISE;
    END IF;
END;

表空间

BEGIN
  EXECUTE IMMEDIATE 'DROP TABLESPACE ' || tablespace_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -959 THEN
      RAISE;
    END IF;
END;

同义词

BEGIN
  EXECUTE IMMEDIATE 'DROP SYNONYM ' || synonym_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -1434 THEN
      RAISE;
    END IF;
END;

2009-11-26 03:58:12

其他回答

我更倾向于指定表和模式所有者。

还要注意大小写敏感性。(见下文“上”条款)。

我扔了几个不同的对象，以表明它可以用在桌子之外的地方。

.............

declare
   v_counter int;
begin
 select count(*) into v_counter from dba_users where upper(username)=upper('UserSchema01');
   if v_counter > 0 then
      execute immediate 'DROP USER UserSchema01 CASCADE';
   end if; 
end;
/



CREATE USER UserSchema01 IDENTIFIED BY pa$$word
  DEFAULT TABLESPACE users
  TEMPORARY TABLESPACE temp
  QUOTA UNLIMITED ON users;

grant create session to UserSchema01;

还有一个TABLE的例子:

declare
   v_counter int;
begin
 select count(*) into v_counter from all_tables where upper(TABLE_NAME)=upper('ORDERS') and upper(OWNER)=upper('UserSchema01');
   if v_counter > 0 then
      execute immediate 'DROP TABLE UserSchema01.ORDERS';
   end if; 
end;
/

2012-08-06 15:23:31

遗憾的是没有，如果存在就删除，如果不存在就创建

您可以编写一个plsql脚本来包含其中的逻辑。

http://download.oracle.com/docs/cd/B12037_01/server.101/b10759/statements_9003.htm

我不太喜欢Oracle语法，但我认为@Erich的脚本应该是这样的。

declare 
cant integer
begin
select into cant count(*) from dba_tables where table_name='Table_name';
if count>0 then
BEGIN
    DROP TABLE tableName;
END IF;
END;

2009-11-25 18:48:18

在oracle中没有'DROP TABLE IF EXISTS'，你必须执行select语句。

试试这个(我不上oracle语法，所以如果我的变量是ify，请原谅我):

declare @count int
select @count=count(*) from all_tables where table_name='Table_name';
if @count>0
BEGIN
    DROP TABLE tableName;
END

2009-11-25 18:49:48

BEGIN
   EXECUTE IMMEDIATE 'DROP TABLE ' || table_name;
EXCEPTION
   WHEN OTHERS THEN
      IF SQLCODE != -942 THEN
         RAISE;
      END IF;
END;

齿顶高作为参考，下面是其他对象类型的等效块:

序列

BEGIN
  EXECUTE IMMEDIATE 'DROP SEQUENCE ' || sequence_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -2289 THEN
      RAISE;
    END IF;
END;

View

BEGIN
  EXECUTE IMMEDIATE 'DROP VIEW ' || view_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -942 THEN
      RAISE;
    END IF;
END;

触发

BEGIN
  EXECUTE IMMEDIATE 'DROP TRIGGER ' || trigger_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -4080 THEN
      RAISE;
    END IF;
END;

指数

BEGIN
  EXECUTE IMMEDIATE 'DROP INDEX ' || index_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -1418 THEN
      RAISE;
    END IF;
END;

列

BEGIN
  EXECUTE IMMEDIATE 'ALTER TABLE ' || table_name
                || ' DROP COLUMN ' || column_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -904 AND SQLCODE != -942 THEN
      RAISE;
    END IF;
END;

数据库链接

BEGIN
  EXECUTE IMMEDIATE 'DROP DATABASE LINK ' || dblink_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -2024 THEN
      RAISE;
    END IF;
END;

物化视图

BEGIN
  EXECUTE IMMEDIATE 'DROP MATERIALIZED VIEW ' || mview_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -12003 THEN
      RAISE;
    END IF;
END;

Type

BEGIN
  EXECUTE IMMEDIATE 'DROP TYPE ' || type_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -4043 THEN
      RAISE;
    END IF;
END;

约束

BEGIN
  EXECUTE IMMEDIATE 'ALTER TABLE ' || table_name
            || ' DROP CONSTRAINT ' || constraint_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -2443 AND SQLCODE != -942 THEN
      RAISE;
    END IF;
END;

调度程序工作

BEGIN
  DBMS_SCHEDULER.drop_job(job_name);
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -27475 THEN
      RAISE;
    END IF;
END;

用户/架构

BEGIN
  EXECUTE IMMEDIATE 'DROP USER ' || user_name;
  /* you may or may not want to add CASCADE */
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -1918 THEN
      RAISE;
    END IF;
END;

包

BEGIN
  EXECUTE IMMEDIATE 'DROP PACKAGE ' || package_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -4043 THEN
      RAISE;
    END IF;
END;

过程

BEGIN
  EXECUTE IMMEDIATE 'DROP PROCEDURE ' || procedure_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -4043 THEN
      RAISE;
    END IF;
END;

函数

BEGIN
  EXECUTE IMMEDIATE 'DROP FUNCTION ' || function_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -4043 THEN
      RAISE;
    END IF;
END;

表空间

BEGIN
  EXECUTE IMMEDIATE 'DROP TABLESPACE ' || tablespace_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -959 THEN
      RAISE;
    END IF;
END;

同义词

BEGIN
  EXECUTE IMMEDIATE 'DROP SYNONYM ' || synonym_name;
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -1434 THEN
      RAISE;
    END IF;
END;

2009-11-26 03:58:12

使用SQL*PLUS，你也可以使用每当SQLERROR命令:

WHENEVER SQLERROR CONTINUE NONE
DROP TABLE TABLE_NAME;

WHENEVER SQLERROR EXIT SQL.SQLCODE
DROP TABLE TABLE_NAME;

使用CONTINUE NONE会报告一个错误，但是脚本将继续。使用EXIT SQL。如果出现错误，脚本将被终止。

请参见:每当SQLERROR文档

2016-04-14 12:10:15

Oracle:如果表存在

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