Question

我有以下带有相应列的示例表：

PEOPLE: PERSON_ID, FIRST_NAME, LAST_NAME, GUARDIAN_ID

STATUS: PERSON_ID, STATUS

示例数据：

PEOPLE:
    2345, George, Foreman, null
    4567, Joseph, Galagar, 2345
    5632, Jenner, Shooter, 2345

STATUS:
    2345, DISPATCHED
    4567, PENDING
    5632, PENDING

鉴于上述情况，我希望从PERSON_ID PEOPLE检索FIRST_NAME，其中STATUS是'George'，也是来自STATUS的{{1}}人，最后是这些人中的每个人的孩子数（换句话说，PEOPLE PERSON_ID是GUARDIAN_ID的{{1}}。

我该怎么做？我在这方面非常生疏。这是一个糟糕的例子，但应该有助于解决我的实际问题。

鉴于上述情况，我应该得到以下结果：

2345, DISPATCHED, 2

Answer 1

试试这个：

CREATE TABLE PEOPLE(PERSON_ID INT, FIRST_NAME VARCHAR(25), LAST_NAME VARCHAR(25), GUARDIAN_ID INT);

INSERT INTO PEOPLE VALUES(2345, 'George', 'Foreman', null);
INSERT INTO PEOPLE VALUES(4567, 'Joseph', 'Galagar', 2345);
INSERT INTO PEOPLE VALUES(5632, 'Jenner', 'Shooter', 2345);

CREATE TABLE STATUS(PERSON_ID INT, STATUS VARCHAR(25));

INSERT INTO STATUS VALUES(2345, 'DISPATCHED');
INSERT INTO STATUS VALUES(4567, 'PENDING');
INSERT INTO STATUS VALUES(5632, 'PENDING');

使用Query，我们得到结果：

SELECT P.PERSON_ID
    ,MAX(S.STATUS)STATUS
    ,MAX(D.Counts)[No of Children]
FROM PEOPLE P
JOIN STATUS S ON S.PERSON_ID = P.PERSON_ID
JOIN(SELECT GUARDIAN_ID, COUNT(1)Counts FROM PEOPLE GROUP BY GUARDIAN_ID) D ON D.GUARDIAN_ID = P.PERSON_ID
WHERE P.FIRST_NAME = 'George'
GROUP BY P.PERSON_ID

<强>输出：

PERSON_ID   STATUS      No of Children
2345        DISPATCHED  2

在#SQL Fiddle

中查看此内容

Answer 2

或使其更简单并保存嵌套选择

select p.PERSON_ID, max(s.STATUS) as status, 
sum (case when kids.person_id is null then 0 else 1 end) as num_children
from PEOPLE p
left join PEOPLE kids on kids.GUARDIAN_ID = p.PERSON_ID
join STATUS s on s.PERSON_ID = p.PERSON_ID
where p.FIRST_NAME = 'George'
group by p.PERSON_ID

SQLite -Complex SELECT具有多个连接

2 个答案: