根据连接条件旋转数据时获取空值

Question

我有一个要求，我必须根据 id 加入两个表。我也为此做了小提琴，但有一列 E_CLUBBED_E 填充为空，但理想情况下，它应该匹配 ques_ans 表的 ref_ans_value 列并给出输出，但我得到空值。

原因：我得到空值，因为 ref_ans_id 对于 ref_ques_id 是空值，我正在加入

join ans_ref ar
on ar.ref_ans_id = qa.ref_ans_id

所以这可能是获得空值的原因。

但这是理想的场景，ref_ques_id 23 ref_ans_id 将仅为空，基于此我必须填充 ques_ans 表中的 ref_ans_value。

CREATE TABLE details_1 (
    e_id    NUMBER(10),
    e_name  VARCHAR2(30),
    CONSTRAINT pk_details_1_e_id PRIMARY KEY ( e_id )
);

insert into details_1 values(11,'A');

CREATE TABLE ques_ref (
    ques_id     NUMBER(10),
    code        VARCHAR2(50),
    code_label  VARCHAR2(100),
    constraint pk_ques_ref primary key(ques_id)
);

insert into ques_ref values(3,'changes_exist','Any known changes');
insert into ques_ref values(2,'E_Clubbed','E_id clubbed with other');
insert into ques_ref values(4,'E_impacted','E impacted by other');
insert into ques_ref values(23,'E_Clubbed_with_other','E clubbed with other E');


CREATE TABLE ques_ans (
    ques_ans_id  NUMBER(10),
    ref_ques_id  NUMBER(10),
    ref_ans_id   NUMBER(10),
    ref_ans_value VARCHAR2(100),
    e_id         NUMBER(10),
    CONSTRAINT pk_ques_ans PRIMARY KEY ( ques_ans_id ),
    CONSTRAINT fk_ques_ans FOREIGN KEY ( e_id )
        REFERENCES details_1 ( e_id ),
        constraint fk_ques_and_ques_id foreign key(ref_ques_id)
        references ques_ref (ques_id)
);

insert into ques_ans values(1,3,1,null,11);
insert into ques_ans values(2,2,2,null,11);
insert into ques_ans values(3,4,1,null,11);
insert into ques_ans values(4,23,null,1234,11);



CREATE TABLE ans_ref (
    ref_ans_id  NUMBER(10),
    code        VARCHAR2(10),
    code_value  VARCHAR2(30)
);

insert into ans_ref values(1,'R_Yes','Yes');
insert into ans_ref values(2,'R_No','No');

小提琴：Fiddle

Answer 1

您只需将最后一个内连接更改为表 ans_ref 的左连接 -

select  d.e_id,
        max(case qa.ref_ques_id when 3 then ar.code_value end) changes_exist,
        max(case qa.ref_ques_id when 2 then ar.code_value end) E_Clubbed,
        max(case qa.ref_ques_id when 4 then ar.code_value end) E_impacted,
        max(case qa.ref_ques_id when 23 then qa.ref_ans_value end) E_CLUBBED_E
  from      details_1 d
        join
            ques_ans qa
          on d.e_id = qa.e_id
        left join ans_ref ar
          on ar.ref_ans_id = qa.ref_ans_id
 group by d.e_id

Fiddle.