Question

我有一个表，其中有A，B，C列。

如果A和B（A，B一起是唯一的），我想更新C列，因此伪代码如下：

 python get-pip.py

如何用SQL编写此代码？

Answer 1

我认为您可以使用case表达式：

update table 
    set c = (case when a = 1 and b = 1 then 1000
                  when a = 2 and b = 2 then 2000
                  when a = 3 and b = 3 then 3000
             end)
where (a = 1 and b = 1) or (a = 2 and b = 2) or (a = 3 and b = 3);

Answer 2

多个更新都可以在任何RDBMS中使用

update yourtable set c = 1000 where a = 1 and b = 1
update yourtable set c = 2000 where a = 2 and b = 2
update yourtable set c = 3000 where a = 3 and b = 3

人们会假设UPDATE语句应该非常标准。
但是，从表或子查询进行更新时，语法可能会有所不同。

这在MS Sql Server中有效

update t
set c = q.c
from yourtable t
join (values 
   (1, 1, 1000)
  ,(2, 2, 2000)
  ,(3, 3, 3000)
) q(a, b, c)
on t.a = q.a and t.b = q.b

这在Postgresql中有效

update yourtable t
set c = q.c
from 
(values 
   (1, 1, 1000)
  ,(2, 2, 2000)
  ,(3, 3, 3000)
) q(a, b, c)
where q.a = t.a and q.b = t.b

这在MySql中有效

update yourtable t
join 
(
   select 1 as a, 1 as b, 1000 as c
   union all select 2, 2, 2000
   union all select 3, 3, 3000
) q on q.a = t.a and q.b = t.b
set t.c = q.c

这在Oracle RDBMS中有效

update yourtable t 
set t.c = 
(
   select q.c
   from 
   (
      select 1 as a, 1 as b, 1000 as c from dual
      union all select 2, 2, 2000 from dual
      union all select 3, 3, 3000 from dual
   ) q
   where q.a = t.a and q.b = t.b
)

Answer 3

如果您是说a等于b：

UPDATE t 
SET c = 1000 * a
WHERE a = b;

对于任何rdbms。
参见demo

sql更新多行，每行都有条件

3 个答案: