如何在MySQL的新列中获得两列之间的差异？
让我们首先创建一个带有列的表，我们将为其计算新列中的差-
mysql> create table DemoTable ( Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, LowValue int, HighValue int );
使用插入命令在表中插入一些记录-
mysql> insert into DemoTable(LowValue,HighValue) values(100,200); mysql> insert into DemoTable(LowValue,HighValue) values(300,700); mysql> insert into DemoTable(LowValue,HighValue) values(1000,2000);
以下是使用select语句显示表中所有记录的查询-
mysql> select *from DemoTable;
这将产生以下输出-
+----+----------+-----------+ | Id | LowValue | HighValue | +----+----------+-----------+ | 1 | 100 | 200 | | 2 | 300 | 700 | | 3 | 1000 | 2000 | +----+----------+-----------+ 3 rows in set (0.00 sec)
这是获取2列之间的差的查询-
mysql> select tbl.Id,tbl.LowValue,tbl.HighValue, HighValue-LowValue AS DifferenceBetweenTwoColumns from DemoTable tbl;
这将产生以下输出-
+----+----------+-----------+-----------------------------+ | Id | LowValue | HighValue | DifferenceBetweenTwoColumns | +----+----------+-----------+-----------------------------+ | 1 | 100 | 200 | 100 | | 2 | 300 | 700 | 400 | | 3 | 1000 | 2000 | 1000 | +----+----------+-----------+-----------------------------+ 3 rows in set (0.00 sec)