我们可以将IFNULL和MySQL ORDER BY一起使用吗？

您可以将IFNULL和ORDER BY子句一起使用。语法如下-

SELECT *FROM yourTableName ORDER BY IFNULL(yourColumnName1,yourColumnName2);

为了理解上述语法，让我们创建一个表。创建表的查询如下-

mysql> create table IfNullDemo
   -> (
   -> Id int NOT NULL AUTO_INCREMENT,
   -> ProductName varchar(10),
   -> ProductWholePrice float,
   -> ProductRetailPrice float,
   -> PRIMARY KEY(Id)
   -> );

使用insert命令在表中插入一些记录。查询如下-

mysql> insert into IfNullDemo(ProductName,ProductWholePrice,ProductRetailPrice) values('Product-1',99.50,150.50);
mysql> insert into IfNullDemo(ProductName,ProductWholePrice,ProductRetailPrice) values('Product-2',NULL,76.56);
mysql> insert into IfNullDemo(ProductName,ProductWholePrice,ProductRetailPrice) values('Product-3',105.40,NULL);
mysql> insert into IfNullDemo(ProductName,ProductWholePrice,ProductRetailPrice) values('Product-4',NULL,NULL);
mysql> insert into IfNullDemo(ProductName,ProductWholePrice,ProductRetailPrice) values('Product-5',209.90,400.50);

使用select语句显示表中的所有记录。查询如下-

mysql> select *from IfNullDemo;

以下是输出-

+----+-------------+-------------------+--------------------+
| Id | ProductName | ProductWholePrice | ProductRetailPrice |
+----+-------------+-------------------+--------------------+
|  1 | Product-1   |              99.5 |              150.5 |
|  2 | Product-2   |              NULL |              76.56 |
|  3 | Product-3   |             105.4 |               NULL |
|  4 | Product-4   |              NULL |               NULL |
|  5 | Product-5   |             209.9 |              400.5 |
+----+-------------+-------------------+--------------------+
5 rows in set (0.02 sec)

这是如果为null时要排序的查询-

mysql> select *from IfNullDemo order by ifnull(ProductWholePrice,ProductRetailPrice);

以下是输出-

+----+-------------+-------------------+--------------------+
| Id | ProductName | ProductWholePrice | ProductRetailPrice |
+----+-------------+-------------------+--------------------+
|  4 | Product-4  |               NULL |               NULL |
|  2 | Product-2  |               NULL |              76.56 |
|  1 | Product-1  |               99.5 |              150.5 |
|  3 | Product-3  |              105.4 |               NULL |
|  5 | Product-5  |              209.9 |              400.5 |
+----+-------------+-------------------+--------------------+
5 rows in set (0.00 sec)