Oracle 11g中的更新

Question

我必须更新表中的字段.我正在使用以下查询.帮助我,哪一个是对的？

update table1
set col1=<value>,col2=<value>....
from table1 t,table2 s
where t.id=s.num
  and s.code='abc';

要么

update table1
set col1=<value>,col2=<value>....
where table1.id=table2.num
  and table2.code='abc';

哪一个是对的？或两者都不正确？请提出一些建议......

Answer 1

两者都不正确.从你的片段中不清楚你要做什么,但用另一个表更新一个表的语法更像是:

update table1
set (col1, col2) =
( select col1, col2
  from   table2
  where  table2.num = table1.id
  and    table2.code = 'abc'
)
where table1.id in (select num from table2);

最后的WHERE子句是为了防止使用null更新所有不匹配的table1行.

当table1 在查询中"密钥保留"时,另一种方法是:

update
( select table1.id, table1.col1, table1.col2
  ,      table2.col1 as new_col1, table2.col as new_col2
  from   table1
         join table2 on table2.num = table1.id
)
set col1 = new_col1, col2 = new_col2;

Answer 2

MERGE
INTO table1 t1
USING (
 SELECT *
 FROM table2
 WHERE table2.code = 'abc'
) t2
ON (t1.id = t2.num)
WHEN MATCHED THEN
  UPDATE
  SET col1 = t2.value1, col2 = t2.value2

请记住始终限定SET语句,即t2.value1.不明确时不会抛出任何错误.换句话说,SET col1 = value1将是t2.value1,但如果缺少t2.value1则为t1.value1.