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