Oracle SQL 计算多个表中的相同字段

Question

我有一个 oracle 数据库，在多个 table 中具有相同的名称字段。它看起来像这样：

table1     table2     table3     table4
field      field      field      field

每个 table 中的公共字段可以是 'yes'、'no' 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

目前我有这个，但它只适用于一个 table，而不适用于多个。

select field, count(*) as table1_cnt
from table1
group by field
_____________________________________
field     table1_cnt
yes       20
no        35
null      8  

Answer 1

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

Answer 2

我想我会推荐使用 union all 和聚合：

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, 0, 1, 0, 0 from table2) union all
      (select field, 0, 0, 1, 0 from table3) union all
      (select field, 0, 0, 0, 1 from table4) 
     ) t
group by field;

与使用 left joins 相比，这具有三个优势：

1. 所有 字段值都包含在结果中，而不仅仅是第一个 table.
中的值
2. NULL 个值包含在结果中。
3. 0 值包含在适当的地方（而不是 NULL 计数）。