判断表是否删除（MySQL、ORACLE）

不同数据库中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中先判断表是否存在再新建表一例：

[c-sharp] view plain copy

print ?

declare
v_exists number;
begin
–1、任务类型 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 ’‘任务类型’”;
execute immediate ’comment on column EDW_T99_TASK_TYPE_CD.CODE_CD is ’‘代码’”;
execute immediate ’comment on column EDW_T99_TASK_TYPE_CD.CODE_DESC is ’‘代码描述’”;
–2、买入产品代码 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 ’‘买入产品代码’”;
execute immediate ’comment on column EDW_T99_BUY_TYPE_CD.CODE_CD is ’‘代码’”;
execute immediate ’comment on column EDW_T99_BUY_TYPE_CD.CODE_DESC is ’‘代码描述’”;
end;
/

declare v_exists number; begin –1、任务类型 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 ”任务类型”’; execute immediate ‘comment on column EDW_T99_TASK_TYPE_CD.CODE_CD is ”代码”’; execute immediate ‘comment on column EDW_T99_TASK_TYPE_CD.CODE_DESC is ”代码描述”’; –2、买入产品代码 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 ”买入产品代码”’; execute immediate ‘comment on column EDW_T99_BUY_TYPE_CD.CODE_CD is ”代码”’; execute immediate ‘comment on column EDW_T99_BUY_TYPE_CD.CODE_DESC is ”代码描述”’; end; /

此例用在数据仓库项目的建T99代码表脚本方案上；此脚本在方案中用Perl根据Excel生成。

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转载地址:https://blog.csdn.net/nsj820/article/details/6308420