Mysql 如何编写一个包含3个表、相同列以及其中一个不同列的查询来执行

我有3个表，其中3个表有3个相同的列名
但是第三个表的第三列与第一个表的第二列不同。
我的需要将澄清给定的图像和查询

//this the query I'm using but not I wanted
select l.admission_number,l.student_class ,l.student_name ,l.telugu  from lkg_to_seventh_marks as l 
union all 
select e.admission_number ,e.student_class ,e.student_name ,e.telugu  from eighth_to_ninth_marks as e 
union all
select t.admission_number ,t.student_class ,t.student_name,t.telugu_1  from tenthclass_marks as t

像这样试试

select l.admission_number,l.student_class ,l.student_name,l.telugu,NULL as telugu_1 
from lkg_to_seventh_marks as l 
union all 
select e.admission_number ,e.student_class ,e.student_name ,e.telugu ,NULL  as telungu_1
from eighth_to_ninth_marks as e 
union all
select t.admission_number ,t.student_class ,t.student_name,NULL as telugu, t.telugu_1 
from tenthclass_marks as t

我想你想要这个问题吗

select l.admission_number,l.student_class ,l.student_name,cast(l.telugu as char(50))
,'NULL' as telugu_1  from lkg_to_seventh_marks as l 
union all 
select e.admission_number ,e.student_class ,e.student_name ,cast(e.telugu as char(50))
,'NULL'as telungu_1
from eighth_to_ninth_marks as e 
union all
select t.admission_number ,t.student_class ,t.student_name,'NULL'as telugu, 
cast(t.telugu_1 as char(50)) as telungu_1
rom tenthclass_marks as t

这可能有用

select l.admission_number,l.student_class ,l.student_name,l.telugu,null as telugu_1 from lkg_to_seventh_marks as l union all select e.admission_number ,e.student_class ,e.student_name ,e.telugu ,null as telungu_1 from eighth_to_ninth_marks as e union all select t.admission_number ,t.student_class ,t.student_name,0 as telugu, t.telugu_1 from tenthclass_marks as t

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我们可以得到一个空字符串而不是空单元格中的0值吗？我们可以得到一个空文本而不是空单元格中的0值吗？？如果您得到一个查询，请添加一个查询idea@ShivaDebrown对你来说没关系，或者你想改变什么？是的。。我只想将文本放置为NULL，如果使用相同的查询将数据加载到datagridview，则datagridview单元格在NULL文本中不可见，单元格仅为空。如果我使用相同的查询将数据加载到datagridview，我希望datagridview单元格中的文本为空。此查询为前两个表提供空值。如果我将相同的查询加载到datagridview，则datagridview单元格将显示空单元格，而不是填充空文本。对于此更改，请将NULL更改为“”（空引号）.空引号给出0值