如何实现 MySQL ORDER BY x where (x=col3 if col3!=null, else x=col2)?
mysqlmysqli database更新于 2024/1/30 14:23:00
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 语句显示表中的所有记录 −
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)
下面是实现 MySQL ORDER BY x 的查询，其中(x=col3 if col3!=null, else 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)
