Merge Into 语法支持

KINGBASE 兼容Oracle 语法，实现了merge into 的功能。以下以例子的形式，介绍merge into语法的使用。以下例子在V8R6 ，且 database_mode=oracle 环境下验证过，database_mode=pg 不支持merge into 语法。

一、创建测试数据

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create table source_table(s_id integer,s_name char(9)); create table target_table(t_id integer,t_name char(9));   insert into source_table values(1,'s_a'),(2,'s_b'); insert into target_table values(1,'t_a'),(3,'t_c');   test=# select * from source_table ; s_id | s_name ------+----------- 1 | s_a 2 | s_b (2 rows)   test=# select * from target_table ; t_id | t_name ------+----------- 1 | t_a 3 | t_c (2 rows)

二、测试例子

1、例子1

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test=# begin; BEGIN test=# merge into target_table as t test-# using source_table as s test-# on (t.t_id=s.s_id) test-# when matched then update set t.t_name=s.s_name test-# when not matched then insert values(s.s_id,s.s_name); MERGE 2   test=# select * from target_table order by t_id; t_id | t_name ------+----------- 1 | s_a 2 | s_b 3 | t_c (3 rows)   test=# rollback; ROLLBACK

注意：更新的列不能是ON 条件中被引用的列。

2、例子2

更新时可以通过WHERE 条件指明要更新的行，条件中既可以包含源表的列，也可以包含目标表的列，当指明WHERE 条件且条件为假时，则不更新。

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test=# begin; BEGIN test=# merge into target_table as t test-# using source_table as s test-# on (t.t_id=s.s_id) test-# when matched then update set t.t_name=s.s_name where t.t_id=3 test-# when not matched then insert values(s.s_id,s.s_name); MERGE 1 test=#   test=# select * from target_table order by t_id;  t_id |  t_name   ------+-----------     1 | t_a        --没有被更新     2 | s_b          3 | t_c      (3 rows)   test=# rollback; ROLLBACK

3、例子3

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test=# begin; BEGIN test=# merge into target_table as t test-# using source_table as s test-# on (t.t_id=s.s_id) test-# when matched then update set t.t_name=s.s_name test-#    delete where t.t_name='s_a' test-# when not matched then insert values(s.s_id,s.s_name); MERGE 3 test=# select * from target_table order by t_id;  t_id |  t_name   ------+-----------     2 | s_b          3 | t_c      (2 rows)   test=# rollback; ROLLBACK

DELETE 子句只删除目标表和源表的ON 条件为真、并且是更新后的符合删除条件的记录，DELETE 子句不影响INSERT 项插入的行

三、Postgresql 实现类 merge into 的方法

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test=# begin; BEGIN test=# with upsert as ( test(#     update target_table test(#     set t_name = source_table.s_name test(#     from source_table test(#     where target_table.t_id = source_table.s_id test(#     returning target_table.* test(# ) test-# insert into target_table select * from source_table test-# where not exists ( test(#     select 1 test(#     from upsert b test(#     where source_table.s_id = b.t_id test(# ); INSERT 0 1 test=# select * from target_table order by t_id;  t_id |  t_name   ------+-----------     1 | s_a          2 | s_b          3 | t_c      (3 rows)   test=# rollback; ROLLBACK