Question

我有两个表：

CREATE TABLE Test_Persons_A (
    PersonID int,
    LastName varchar(255),
    FirstName varchar(255)
);

INSERT INTO Test_Persons_A
    (PersonID,LastName,FirstName)
    values(11,'LN_A1','FN_A1');

INSERT INTO Test_Persons_A
    (PersonID,LastName,FirstName)
    values(12,'LN_A2','FN_A2');

CREATE TABLE Test_Persons_B (
    PersonID int,
    LastName varchar(255),
    FirstName varchar(255)
);

INSERT INTO Test_Persons_B
    (PersonID,LastName,FirstName)
    values(21,'LN_B1','FN_B1');

INSERT INTO Test_Persons_B
    (PersonID,LastName,FirstName)
    values(22,'LN_B2','FN_B2');

commit;

但是后来我不知道如何对随后的“ WITH”进行条件选择：

------------------------------use IF, not working ------------------------------
var TEST_TBL varchar2(20);
exec :TEST_TBL := 'test_person_A';

with Test_tbl as
(
    IF UPPER(:TEST_TBL) = 'TEST_PERSONS_A' then select * from Test_Persons_A;
    ELSIF UPPER(:TEST_TBL) = 'TEST_PERSONS_B' then select * from Test_Persons_B;
    End if;
)

select PersonID as PID, LastName as LN, FirstName as FN
    from Test_tbl tp
    where tp.LASTNAME like '%1%'

------------------------------use CASE, not working ------------------------------
var TEST_TBL varchar2(20);
exec :TEST_TBL := 'test_person_A';

with Test_tbl as
(
    CASE WHEN UPPER(:TEST_TBL) = 'TEST_PERSONS_A' then 
        select * from Test_Persons_A;
    ELSE 
        select * from Test_Persons_B;
    End
)
select PersonID as PID, LastName as LN, FirstName as FN
    from Test_tbl tp
    where tp.LASTNAME like '%1%';

最终，我可以以某种方式概括一下吗？即在SQL（至少是Oracle）中，我可以在哪里断言条件语句，而我不能在哪里断言？

Answer 1

使用union all：

with Test_tbl as (
      select *
      from Test_Persons_A
      where upper(:TEST_TBL) = 'TEST_PERSONS_A' 
      union all
      select *
      from Test_Persons_B
      where UPPER(:TEST_TBL) = 'TEST_PERSONS_B'
     )

这假定表具有相同顺序的相同列。

如果它们没有相同的列，请列出其余代码所需的特定列，也许将NULL分配给可能不在其中一个表中的列。

Oracle SQL：在“ WITH”语句中，如何进行条件选择，使用IF或CASE？

1 个答案: