oracle update join

今天需要写一个根据关联查询结果更新数据的sql,mysql中支持这样的语法:

mysql:

UPDATE T1, T2,
[INNER JOIN | LEFT JOIN] T1 ON T1.C1 = T2. C1
SET T1.C2 = T2.C2, 
    T2.C3 = expr
WHERE condition

但是oracle不支持上面的语法,oracle实现上面功能的语法结构如下:

oracle 方式1:

UPDATE table1 
  SET table1.value = (SELECT table2.CODE 
                      FROM table2 
                      WHERE table1.value = table2.DESC)
WHERE table1.UPDATETYPE='blah'
AND EXISTS (SELECT table2.CODE
            FROM table2 
            WHERE table1.value = table2.DESC);

或者

oracle 方式2:

UPDATE 
(SELECT table1.value as OLD, table2.CODE as NEW
 FROM table1
 INNER JOIN table2
 ON table1.value = table2.DESC
 WHERE table1.UPDATETYPE='blah'
) t
SET t.OLD = t.NEW

实际上面在线上环境执行,风险还是比较高的,比较推荐还是直接输出执行脚本后执行,这样就算有问题也可以将问题范围控制在脚本范围内;

SELECT 'update table_update set field='''||update_field||''',ts=to_char(sysdate,''yyyy-mm-dd hh24:mi:ss'') where key_field='''||query_field||''';' 
from(
  select query_field_key,update_field from table1 t1 
  inner join table2 t2
  on t1.field=t2.field 
)

方式3: merge into

merge into <update_table>  b
using <relation_table> a
on (a.CODE=b.CODE )
when matched then 
	update set b.DESCRIPTION=a.DESCRIPTION
	[delete where (a.CODE='2')]
when not matched then
	insert values (a.NAME, a.CODE, a.DESCRIPTION,a.THRDR) where a.CODE = '1'

复杂更新操作,备份是基础.要做好随时删库跑路的准备.

参考资料:

[merge into] https://blog.csdn.net/naomi_qing/article/details/70785702