如何将多个 SQL 查询合并为一个？

Question

我有多个 sql 查询，我想将它们捆绑到一个查询中，这样我就可以避免从我的应用程序向数据库发送多个请求（我想一次性接收所有这些数据）：

1) select pin, officeNum, isVeteran from table18 where pin = 123;

2) select streetAddress, apartmentAddress, cityAddress, stateAddress from table1 where case = (select case from table18 where pin = 123);

3) select unitAddress, cityAddress, streetAddress, apartmentAddress from table5 where pin = 123;

4) select unitAddress, cityAddress, streetAddress, apartmentAddress from table55 where seqNum = 0 and rfa = (select rfa from table18 where pin = 123);

5) select unitAddress, cityAddress, streetAddress, apartmentAddress from table103 where histCode = 0 and case = (select case from table18 where pin = 123);

6) select phone, email from table715 where histSeqNum in (select max(histSeqNum from table715))
      and histCode in (select max(histCode) from table715)
      and case = (select case from table18 where pin = 123);

这是我的架构：

（请原谅不好的设计，它来自20年前创建的数据库，没有外键）

-Table18（引脚（PK）、案例、officeNum、isVeteran）

-Table1（案例（PK）、案例官员、街道地址、公寓地址、城市地址、州地址）

-Table5（引脚（PK）、街道地址、公寓地址、城市地址、州地址）

-Table55（rfa（复合键），seqNum（复合键），rfa地址，街道地址，公寓地址，城市地址，州地址）

-Table103（案例（CompositeKey），histCode（CompositeKey））

-Table715（案例（CompositeKey）、histSeqNum（CompositeKey）、histCode（CompositeKey）、电话、电子邮件）

Answer 1

这是一个可以合并的集合... (3,4,5)

select unitAddress, cityAddress, streetAddress, apartmentAddress 
from table5 where pin = 123
union
select unitAddress, cityAddress, streetAddress, apartmentAddress 
from table55 where seqNum = 0 and rfa = (select rfa from table18 where pin = 123)
union
select unitAddress, cityAddress, streetAddress, apartmentAddress 
from table103 where histCode = 0 and case = (select case from table18 where pin = 123);

如果你不介意这些上的空白状态，你也可以把（2）放在那里......

例如，在 2 中写下如下内容：

select null unitAddress, streetAddress, apartmentAddress, cityAddress, stateAddress 
from table1 
where case = (select case from table18 where pin = 123);
union
select unitAddress, cityAddress, streetAddress, apartmentAddress, null
from table5 where pin = 123
union
select unitAddress, cityAddress, streetAddress, apartmentAddress, null 
from table55 where seqNum = 0 and rfa = (select rfa from table18 where pin = 123)
union
select unitAddress, cityAddress, streetAddress, apartmentAddress, null
from table103 where histCode = 0 and case = (select case from table18 where pin = 123);

还考虑将嵌套选择重组为连接 - 类似于此：（我打赌优化这些查询将是您正在寻找的性能差异）

select streetAddress, apartmentAddress, cityAddress, stateAddress 
from table1  t1, table18 t18
where t1.case = t18.case 
and t18.123;

然后确保 t18 在引脚上有索引，并且 t1 在外壳上有索引。