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)