仅返回表中的非空值和非空值，并在MySQL中用相应的列值填充空值和NULL值？

让我们首先创建一个表-

mysql> create table DemoTable839(
   StudentFirstName varchar(100),
   StudentLastName varchar(100)
);

使用插入命令在表中插入一些记录-

mysql> insert into DemoTable839 values('Chris','Brown');
mysql> insert into DemoTable839 values('','Taylor');
mysql> insert into DemoTable839 values(NULL,'Taylor');
mysql> insert into DemoTable839 values('Adam','Smith');

使用select语句显示表中的所有记录-

mysql> select *from DemoTable839;

这将产生以下输出-

+------------------+-----------------+
| StudentFirstName | StudentLastName |
+------------------+-----------------+
| Chris            | Brown           |
|                  | Taylor          |
| NULL             | Taylor          |
| Adam             | Smith           |
+------------------+-----------------+
4 rows in set (0.00 sec)

以下是查询，仅从表中返回非空和非空值，并用相应的列值填充空值和空值-

mysql> select if(length(StudentFirstName),StudentFirstName,StudentLastName) from DemoTable839;

这将产生以下输出-

+---------------------------------------------------------------+
| if(length(StudentFirstName),StudentFirstName,StudentLastName) |
+---------------------------------------------------------------+
| Chris                                                         |
| Taylor                                                        |
| Taylor                                                        |
| Adam                                                          |
+---------------------------------------------------------------+
4 rows in set (0.00 sec)