Mysql中判断两个数值大小 并赋值

Question

在一个表(t1)中有三个字段(field1,field2,field3),如果field1>field2,那么field3的值为field1,如果field1<=field2,那么field3的值为field2

Answer 1

是根据field1和field2的最大值，更新字段field3吗？

update t1 set field3 = GREATEST(field1, field2)

Answer 2

sqlserver的话简单的case就能实现

UPDATE [TableName] SET Field3=
(
  CASE 
      WHEN Field1>Field2 THEN Field1
      WHEN Field1<Field2 THEN Field2
      WHEN Field1=Field2 THEN Field2
   END
) 

Answer 3

可以配合php使用if判断嘛。。或三元运算
field1>field2:field3 = field1 ? field3 = field2