MySQL 如何实现 MySQL ORDER BY x，其中(x = col3 if col3！= null，否则x = col2)

为此，您可以使用 ORDER BY IFNULL()。让我们首先创建一个表 –

mysql> create table DemoTable
     -> (
     -> Name varchar(20),
     -> CountryName varchar(20)
     -> );
Query OK, 0 rows affected (0.61 sec)

使用 insert 命令在表中插入一些记录 –

mysql> insert into DemoTable values('Chris',NULL);
Query OK, 1 row affected (0.19 sec)
mysql> insert into DemoTable values('David','AUS');
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable values(NULL,'UK');
Query OK, 1 row affected (0.17 sec)
mysql> insert into DemoTable values(NULL,'AUS');
Query OK, 1 row affected (0.10 sec)
mysql> insert into DemoTable values(NULL,NULL);
Query OK, 1 row affected (0.11 sec)

使用 select 语句显示来自表的所有记录 –

mysql> select *from DemoTable;

这将产生以下输出 –

+-------+-------------+
| Name  | CountryName |
+-------+-------------+
| Chris | NULL        |
| David | AUS         |
| NULL  | UK          |
| NULL  | AUS         |
| NULL  | NULL        |
+-------+-------------+
5 rows in set (0.00 sec)

这是实现 MySQL ORDER BY x 的查询，其中(x = col3 if col3！= null，否则x = col2) –

mysql> select *from DemoTable
     -> order by ifnull(Name,CountryName);

这将产生以下输出 –

+-------+-------------+
| Name  | CountryName |
+-------+-------------+
| NULL  | NULL        |
| NULL  | AUS         |
| Chris | NULL        |
| David | AUS         |
| NULL  | UK          |
+-------+-------------+
5 rows in set (0.00 sec)

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