更新表 - Mysql

Question

需要更新列c2以获取相同c3的所有值。即c3有五个0，前三个0有c在10。在这里，我需要用值10更新记录7和9.最后，c3中的所有0都应该具有相同的c2值，即10

Answer 1

您需要self join，然后将列C2更新为：

UPDATE table_name a
       INNER JOIN table_name b
           ON a.C2 = b.C3
SET a.C2 = b.C2
WHERE b.C2 <> 0;

Answer 2

您如何决定从哪个记录中获取更新其他记录？ select c3 from yourTable group by c3将返回您的不同c3值，现在您可以获得每个c3的相应c2值，但是您想如何决定使用哪个值来更新其他值？

编辑：
很少有SQL语句接近：
set @uniqueC3s = (select c3 from yourTable group by c3);
-- loop through the resutlset set @requiredC2Value = (select TOP 1 c2 from yourTable where c3 = @uniqueC3s order by c1);
update yourTable set c2 = @requiredC2Value where c3 = @uniqueC3s;
-- end of loop