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ORACLE 9I中加入了MERGE 语法: MERGE [hint] INTO [schema .] table [t_alias] USING [schema .] { table | view

  Oracle 9I中加入了MERGE

  语法:

  MERGE [hint] INTO [schema .] table [t_alias]

  USING [schema .] { table | view | subquery } [t_alias]

  ON ( condition )

  WHEN MATCHED THEN merge_update_clause

  WHEN NOT MATCHED THEN merge_insert_clause;

  创建测试数据表:

  create table tj_test(id number,name varchar2(20),age number);

  向表中插入数据:

  insert into tj_test values (1,'jan',23);

  insert into tj_test values (2,'kk',22);

  insert into tj_test values (3,'joe',27);

  select * from tj_test;

  查询结果如下:

  1 jan 23

  2 kk 22

  3 joe 27

  创建另一新表

  create table tj_test1 as select * from tj_test where 1=0

  插入一条数据

  insert into tj_test1 values (1,'jlk',23);

  select * from tj_test1

  查询结果如下:

  1 jkl 23 --注意,这里的的NAME字段中的值是jkl

  使用MERGE,实现有则更新,无则插入,sql语句如下:

  merge into tj_test1 tt1

  using tj_test tt

  on (tt1.id=tt.id)

  when matched then

  update set

  tt1.name=tt.name,

  tt1.age=tt.age

  when not matched then

  insert values(

  tt.id,

  tt.name,

  tt.age)

  查询tj_test1表(对比原来表中的数据,更新了ID=1 ROW中字段NAME,同时多出两条新数据)

  select * from tj_test1

  改变行数据如下:

  1 jan 23 --这里的原有jkl值被更新

  3 joe 27 --原来表中没有的插入

  2 kk 22 --原来表中没有的插入

  如果存在就更新,不存在就插入

  9i已经支持了,是Merge,但是只支持select子查询,

  如果是单条数据记录,,可以写作select …… from dual的子查询。

  语法为:

  MERGE INTO table

  USING data_source

  ON (condition)

  WHEN MATCHED THEN update_clause

  WHEN NOT MATCHED THEN insert_clause;

  如:

  MERGE INTO course c

  USING (SELECT course_name, period,

  course_hours

  FROM course_updates) cu

  ON (c.course_name = cu.course_name

  AND c.period = cu.period)

  WHEN MATCHED THEN

  UPDATE

  SET c.course_hours = cu.course_hours

  WHEN NOT MATCHED THEN

  INSERT (c.course_name, c.period,

  c.course_hours)

  VALUES (cu.course_name, cu.period,

  cu.course_hours);

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