Question

mysql服务器版本：mysql 5.6 客户端：datagrip

我期望的sql是

select * from user GROUP BY level;

但我错误地执行了

select * from user GROUP BY level=1;

我认为mysql会抛出一个错误，但它不会。和mysql给我一行。

为什么？

Answer 1

它将返回表格的最后一行和匹配的行，其中level = 1.

例如：

CategoryID    CategoryName      Description
1             Beverages         Soft drinks, coffees, teas, beers, and ales
2             Condiments        Sweet and savory sauces, relishes, spreads, and seasonings
3             Confections       Desserts, candies, and sweet breads
4             Dairy Products    Cheeses
5             Grains/Cereals    Breads, crackers, pasta, and cereal
6             Meat/Poultry      Prepared meats
7             Produce           Dried fruit and bean curd
8             Seafood           Seaweed and fish

以下查询：

SELECT CategoryID,CategoryName,Description FROM Categories GROUP BY CategoryID = 3

将导致：

CategoryID  CategoryName    Description
8            Seafood        Seaweed and fish
3            Confections    Desserts, candies, and sweet breads

expresssion field = xxx after group by

1 个答案: