Question

联接两个表并返回第二个表的第一条记录-拥有此代码。第二个表中的一列可以具有相同的值。如果是这样，则返回该值；否则返回0。否则，返回null。

使用了distinct，但即使列值不是distinct（即返回null），仍需要返回第一条记录

CREATE TABLE Person ("LAST_NAME" VARCHAR2(50 BYTE), 
"TICKET_NUMBER" VARCHAR2(50 BYTE));
BEGIN
insert into Person(last_name,ticket_number) values('johnson','100');
insert into Person(last_name,ticket_number) values('smith','200');
END;
/

CREATE TABLE Orders 
("REGION" VARCHAR2(50 BYTE), 
"STATE" VARCHAR2(50 BYTE), 
"A_CODE" VARCHAR2(5 BYTE),
"STORE_NUM" VARCHAR2(50 BYTE), 
"TICKET_NUMBER" VARCHAR2(50 BYTE),
"SEQ" NUMBER(12));

SELECT a.last_name,
     a.ticket_number,
     b.region,
     b.state,
     b.SEQ1,
     B.A_CODE
FROM person a

BEGIN
insert into Orders(ticket_number, REGION, STATE, STORE_NUM, A_CODE, SEQ ) 
values('100', 'S', 'F1', '111', 'FLL', 1);
insert into Orders(ticket_number, REGION, STATE, STORE_NUM, A_CODE, SEQ ) 
values('100', 'S', 'F1', '222', 'FLL', 2);
insert into Orders(ticket_number, REGION, STATE, STORE_NUM, A_CODE, SEQ ) 
values('100', 'S', 'F1', '333', 'FLL', 3);
insert into Orders(ticket_number, REGION, STATE, STORE_NUM, A_CODE, SEQ ) 
values('100', 'S', 'F1', '444', 'FLL', 4);

END;
/


JOIN (SELECT ticket_number, MIN(SEQ) AS SEQ1,
        MIN(region) AS region,
        MIN(state) AS state, MIN(A_CODE) AS A_CODE
 FROM orders WHERE REGION IS NOT NULL
 GROUP BY ticket_number) b ON a.ticket_number = b.ticket_number where 
  a.last_name is not null;

A_CODE值相同-返回值

LAST_NAME   TICKET_NUMBER   REGION  STATE   SEQ1    A_CODE
johnson         100           S       F1      1       FLL

但是，如果A_CODE的值不是唯一的（即不相同），则对于A_CODE列返回null，并且仍然返回第二个表的第一条记录。注意：作为一种选择，如果不相等，则列值不需要返回null。它可以返回“不等于”之类的文字

LAST_NAME   TICKET_NUMBER   REGION  STATE   SEQ1    A_CODE
johnson      100             S       F1     1         (NULL)

Oracle Database 12c企业版12.2.0.1.0版-64位生产

Answer 1

下面是查询

SELECT a.last_name,
     a.ticket_number,
     b.region,
     b.state,
     b.SEQ1,
     case when B.MIN_A_CODE = B.MAX_A_CODE then B.MIN_A_CODE else 'NULL' end A_CODE
FROM person a
JOIN ( SELECT ticket_number, MIN(SEQ) AS SEQ1,
        MIN(region) AS region,
        MIN(state) AS state, MIN(A_CODE) AS MIN_A_CODE, max(A_CODE) as MAX_A_CODE
 FROM orders WHERE REGION IS NOT NULL
 GROUP BY ticket_number) b ON a.ticket_number = b.ticket_number where 
  a.last_name is not null;

我在表格订单中又增加了一行。

insert into Orders(ticket_number, REGION, STATE, STORE_NUM, A_CODE, SEQ ) 
values('100', 'S', 'F1', '111', 'FLL', 1);
insert into Orders(ticket_number, REGION, STATE, STORE_NUM, A_CODE, SEQ ) 
values('100', 'S', 'F1', '222', 'FLL', 2);
insert into Orders(ticket_number, REGION, STATE, STORE_NUM, A_CODE, SEQ ) 
values('100', 'S', 'F1', '333', 'FLL', 3);
insert into Orders(ticket_number, REGION, STATE, STORE_NUM, A_CODE, SEQ ) 
values('100', 'S', 'F1', '444', 'FLL', 4);
insert into Orders(ticket_number, REGION, STATE, STORE_NUM, A_CODE, SEQ ) 
values('100', 'S', 'F1', '444', 'DLL', 4);

O / p-

LAST_NAME   TICKET_NUMBER   REGION  STATE   SEQ1    A_CODE
johnson 100 S   F1  1   NULL

我的理解是，对于同一区域，您具有不同的A_CODE，因此您需要为A_CODE输入null，但所有其他列的值都应该是第一条记录。

希望这会有所帮助

联接表-仅返回第一条记录和唯一的列（如果存在），否则返回空列

1 个答案: