请问一个简单的连接查询的有关问题。多谢
请教一个简单的连接查询的问题。谢谢
现有表1表2
table11,table2
table1:
id value1
1 100
2 200
3 700
table2:
id value2
1 98
3 99
我想得到的查询结果为
id value1 value2
1 100 98
2 200 0 (或者显示null也行)
3 700 99
sql该如何写?
而我实际得到结果中没有2号记录。
------解决方案--------------------
现有表1表2
table11,table2
table1:
id value1
1 100
2 200
3 700
table2:
id value2
1 98
3 99
我想得到的查询结果为
id value1 value2
1 100 98
2 200 0 (或者显示null也行)
3 700 99
sql该如何写?
而我实际得到结果中没有2号记录。
------解决方案--------------------
- SQL code
select a.id,a.value1,b.value2 from table1 a left join table2 b on a.id=b.id
------解决方案--------------------
- SQL code
select isnull(a.id,b.id) as id,isnull(a.value1,0) as value1, isnull(b.value2,0) as value2 from table1 a full join table2 b on a.id=b.id
------解决方案--------------------
select tbl1.id,tbl1.value1,tbl2.value2 from tbl1 left join tbl2 on tbl1.id=tbl2.id
用左连接查询,你可能用了内连接
------解决方案--------------------
- SQL code
if object_id('table1') is not null drop table table1 go create table table1 ( id int, value1 int ) go insert into table1 select 1,100 union all select 2,200 union all select 3,700 go if object_id('table2') is not null drop table table2 go create table table2 ( id int, value2 int ) go insert into table2 select 1,98 union all select 3,99 go select a.id,a.value1,b.value2 from table1 a left join table2 b on a.id=b.id --显示null select a.id,a.value1,value2=isnull(b.value2,0) from table1 a left join table2 b on a.id=b.id --显示0 /* id value1 value2 ----------- ----------- ----------- 1 100 98 2 200 0 3 700 99 (3 行受影响) */
------解决方案--------------------
- SQL code
create table table1(id int,value1 int) insert into table1 select 1,100 insert into table1 select 2,200 insert into table1 select 3,700 create table table2(id int,value2 int) insert into table2 select 1,98 insert into table2 select 3,99 go select a.id,a.value1,b.value2 from table1 a left join table2 b on a.id=b.id /* id value1 value2 ----------- ----------- ----------- 1 100 98 2 200 NULL 3 700 99 (3 行受影响) */ go drop table table1,table2
------解决方案--------------------