不同數(shù)據(jù)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';

ifv_exists?>?0?then

execute?immediate'drop?table?EDW_T99_TASK_TYPE_CD';

endif;

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(chǎn)品代碼?BUY_TYPE_CD?建表...

select?count(*)?into?v_exists?from?user_tables?where?table_name?='EDW_T99_BUY_TYPE_CD';

ifv_exists?>?0?then

execute?immediate'drop?table?EDW_T99_BUY_TYPE_CD';

endif;

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(chǎn)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;

/

此例用在數(shù)據(jù)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(jù)Excel生成。

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