Firebird 用查询结果集更新数据，merge

Merge语法：

 MERGE INTO  target [[AS]  target-alias ]
 USING  source [[AS]  source-alias ]
 ON  join-condition
 WHEN MATCHED THEN UPDATE SET  colname =  value [,  colname =  value ...]
 WHEN NOT MATCHED THEN INSERT [( <columns> )] VALUES ( <values> )

例子A：

 MERGE INTO books b
 USING purchases p
 ON p.title = b.title and p.type = 'bk'
 WHEN MATCHED THEN
 UPDATE SET b.desc = b.desc || '; ' || p.desc
 WHEN NOT MATCHED THEN
 INSERT (title, desc, bought) values (p.title, p.desc, p.bought)

例子B：

 MERGE INTO customers c
 USING (SELECT * from customers_delta WHERE id > 10) cd
 ON (c.id = cd.id)
 WHEN MATCHED THEN
 UPDATE SET name = cd.name
 WHEN NOT MATCHED THEN
 INSERT (id, name) values (cd.id, cd.name)

Mysql的语法：注意只能用inner join。

 Update A inner join B on A.xx = B.xx
 Set A.xxx = B.xxx