如何在 MySQL 中获取两个值的最大值？
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How to get the max of two values in MySQL?
提问by Mask
I tried but failed:
我试过但失败了：
mysql> select max(1,0);
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '0)' at line 1
回答by NinethSense
Use GREATEST()
E.g.:
例如：
SELECT GREATEST(2,1);
Note: Whenever if any single value contains null at that time this function always returns null (Thanks to user @sanghavi7)
注意：当任何单个值包含 null 时，此函数始终返回 null（感谢用户 @sanghavi7）
回答by cs_alumnus
To get the maximum value of a column across a set of rows:
要在一组行中获取列的最大值：
SELECT MAX(column1) FROM table; -- expect one result
To get the maximum value of a set of columns, literals, or variables for each row:
要获取每行的一组列、文字或变量的最大值：
SELECT GREATEST(column1, 1, 0, @val) FROM table; -- expect many results
回答by Leonid Zakharov
You can use GREATESTfunction with not nullable fields. If one of this values (or both) can be NULL, don't use it (result can be NULL).
您可以将GREATEST函数与不可为空的字段一起使用。如果此值之一（或两者）可以为 NULL，则不要使用它（结果可以为 NULL）。
select
if(
fieldA is NULL,
if(fieldB is NULL, NULL, fieldB), /* second NULL is default value */
if(fieldB is NULL, field A, GREATEST(fieldA, fieldB))
) as maxValue
You can change NULL to your preferred default value (if both values is NULL).
您可以将 NULL 更改为您首选的默认值（如果两个值都是 NULL）。
