问题描述
我有一个在多个表中具有相同名称字段的oracle数据库。看起来像这样:
table1 table2 table3 table4
field field field field
每个表中的公共字段可以是“是”,“否”或null。我试图在一个查询中获取所有字段的值计数,但我无法弄清楚。基本上我想要这个:
field table1_cnt table2_cnt table3_cnt table4_cnt
yes 20 25 30 35
no 35 25 15 5
null 8 6 7 5
到目前为止,我已经知道了,但是它仅适用于一个表,而不是多个表。
select field,count(*) as table1_cnt
from table1
group by field
_____________________________________
field table1_cnt
yes 20
no 35
null 8
解决方法
您可以尝试使用加入
select t1.field,table1_cnt,table2_cnt,table3_cnt,table4_cnt
from
(
select field,count(*) as table1_cnt
from table1
group by field
)t1 left join
(
select field,count(*) as table2_cnt
from table2
group by field
)t2 on t1.field=t2.field left join
(
select field,count(*) as table3_cnt
from table3
group by field
)t3 on t1.field=t3.field left join
(
select field,count(*) as table4_cnt
from table4
group by field
)t2 on t1.field=t4.field
,
我认为我建议使用union all
并进行汇总:
select field,sum(table_1),sum(table_2),sum(table_3),sum(table_4)
from ((select field,1 as table_1,0 as table_2,0 as table_3,0 as table_4 from table1) union all
(select field,1,0 from table2) union all
(select field,0 from table3) union all
(select field,1 from table4)
) t
group by field;
与使用left join
s相比,这具有三个优点:
- 所有字段值都包括在结果中,而不仅仅是第一张表中的值。
-
NULL
值包含在结果中。 -
0
值包括在适当的位置(而不是NULL
个计数)。