Oracle中的左外联接和计数_Oracle

Oracle中的左外联接和计数

oracle

Oracle中的左外联接和计数,oracle,Oracle,我的导师有以下问题 7）一家博物馆要求提供所有考古学家的名字和姓氏，以及他们发现霸王龙恐龙的地点数量。请注意，一些考古学家没有发现任何恐龙，一些考古学家也没有发现任何霸王龙恐龙，但仍应列入清单我在下面写的声明只向我展示了发现特雷克斯的考古学家。有人能帮我把问题中的所有信息都包括进去吗 SELECT ARCHEOLOGIST.FIRST_NAME, ARCHEOLOGIST.LAST_NAME,DINOSAUR.DINO_NAME, LOCATION.LOCATION_ID, COUNT

我的导师有以下问题 7）一家博物馆要求提供所有考古学家的名字和姓氏，以及他们发现霸王龙恐龙的地点数量。请注意，一些考古学家没有发现任何恐龙，一些考古学家也没有发现任何霸王龙恐龙，但仍应列入清单

我在下面写的声明只向我展示了发现特雷克斯的考古学家。有人能帮我把问题中的所有信息都包括进去吗

 SELECT ARCHEOLOGIST.FIRST_NAME, ARCHEOLOGIST.LAST_NAME,DINOSAUR.DINO_NAME, LOCATION.LOCATION_ID,
  COUNT(LOCATION.LOCATION_ID)AS TOTAL_LOCATIONS
FROM ARCHEOLOGIST
LEFT OUTER JOIN DISCOVERY ON DISCOVERY.ARCH_ID = ARCHEOLOGIST.ARCH_ID
LEFT OUTER JOIN LOCATION ON LOCATION.LOCATION_ID = DISCOVERY.LOCATION_ID
LEFT OUTER JOIN DINOSAUR ON DISCOVERY.DINO_ID = DINOSAUR.DINO_ID
WHERE (DISCOVERY.DINO_ID = 123) 
group by ARCHEOLOGIST.FIRST_NAME, ARCHEOLOGIST.LAST_NAME, DINOSAUR.DINO_NAME, LOCATION.LOCATION_ID;

CREATE TABLE DINOSAUR
(DINO_ID NUMBER(3) PRIMARY KEY,
DINO_NAME VARCHAR2(50) NOT NULL,
DIET_TYPE VARCHAR2(25) NOT NULL,
COST NUMBER(10));

CREATE TABLE LOCATION
(LOCATION_ID VARCHAR2(2) PRIMARY KEY,
LOCATION_NAME VARCHAR2(50) NOT NULL,
STATE_NAME VARCHAR2(50) NOT NULL);

CREATE TABLE ARCHEOLOGIST
(ARCH_ID VARCHAR2(3) PRIMARY KEY,
FIRST_NAME VARCHAR2(25) NOT NULL,
LAST_NAME VARCHAR2(25) NOT NULL);

CREATE TABLE DISCOVERY
(DISC_ID VARCHAR2(3) PRIMARY KEY,
DISC_DATE DATE NOT NULL,
DINO_ID NUMBER(3) NOT NULL,
ARCH_ID VARCHAR2(3) NOT NULL,
LOCATION_ID VARCHAR2(2) NOT NULL);

ALTER TABLE DISCOVERY
ADD CONSTRAINT DINO_ID
FOREIGN KEY (DINO_ID)
REFERENCES DINOSAUR(DINO_ID);

ALTER TABLE DISCOVERY
ADD CONSTRAINT ARCH_ID
FOREIGN KEY (ARCH_ID)
REFERENCES ARCHEOLOGIST(ARCH_ID);

ALTER TABLE DISCOVERY
ADD CONSTRAINT LOCATION_ID
FOREIGN KEY (LOCATION_ID)
REFERENCES LOCATION(LOCATION_ID);

INSERT INTO DINOSAUR
(DINO_ID, DINO_NAME, DIET_TYPE, COST)
VALUES
(123,'TYRANNOSAURUS REX','CARNIVORE',100000);

INSERT INTO DINOSAUR
(DINO_ID, DINO_NAME, DIET_TYPE, COST)
VALUES
(234,'TYRANNOSAURUS REX','CARNIVORE',500000);

INSERT INTO DINOSAUR
(DINO_ID, DINO_NAME, DIET_TYPE, COST)
VALUES
(345,'TYRANNOSAURUS REX','HERBIVORE',250000);

INSERT INTO DINOSAUR
(DINO_ID, DINO_NAME, DIET_TYPE)
VALUES
(456,'TYRANNOSAURUS REX','HERBIVORE');

INSERT INTO DINOSAUR
(DINO_ID, DINO_NAME, DIET_TYPE, COST)
VALUES
(567,'TYRANNOSAURUS REX','HERBIVORE',500000);

INSERT INTO DINOSAUR
(DINO_ID, DINO_NAME, DIET_TYPE, COST)
VALUES
(789,'TYRANNOSAURUS REX','CARNIVORE',750000);

INSERT INTO LOCATION
(LOCATION_ID, LOCATION_NAME, STATE_NAME)
VALUES
('A1','BLACK HILLS','SOUTH DAKOTA');

INSERT INTO LOCATION
(LOCATION_ID, LOCATION_NAME, STATE_NAME)
VALUES
('B2','LOS ANGELES','CALIFORNIA');

INSERT INTO LOCATION
(LOCATION_ID, LOCATION_NAME, STATE_NAME)
VALUES
('C3','GRAND CANYON','ARIZONA');

INSERT INTO LOCATION
(LOCATION_ID, LOCATION_NAME, STATE_NAME)
VALUES
('D4','TAMPA','FLORIDA');

INSERT INTO LOCATION
(LOCATION_ID, LOCATION_NAME, STATE_NAME)
VALUES
('E5','ROME','NEW YORK');

INSERT INTO LOCATION
(LOCATION_ID, LOCATION_NAME, STATE_NAME)
VALUES
('F6','CALGARY','CANADA');

INSERT INTO LOCATION
(LOCATION_ID, LOCATION_NAME, STATE_NAME)
VALUES
('G7','MILWAUKEE','WISCONSIN');

INSERT INTO ARCHEOLOGIST
(ARCH_ID,FIRST_NAME,LAST_NAME)
VALUES
('ABC','ERNEST','HEMINGWAY');

INSERT INTO ARCHEOLOGIST
(ARCH_ID,FIRST_NAME,LAST_NAME)
VALUES
('DEF','AYN','RAND');

INSERT INTO ARCHEOLOGIST
(ARCH_ID,FIRST_NAME,LAST_NAME)
VALUES
('GHI','GRETA','GARBO');

INSERT INTO ARCHEOLOGIST
(ARCH_ID,FIRST_NAME,LAST_NAME)
VALUES
('JKL','FRED','ASTAIRE');

INSERT INTO ARCHEOLOGIST
(ARCH_ID,FIRST_NAME,LAST_NAME)
VALUES
('MNO','GINGER','ROGERS');

INSERT INTO DISCOVERY
(DISC_ID, DISC_DATE, DINO_ID, ARCH_ID, LOCATION_ID)
VALUES
('Z12',TO_DATE('12/12/2010','MM/DD/YYYY'),123,'ABC','A1');

INSERT INTO DISCOVERY
(DISC_ID, DISC_DATE, DINO_ID, ARCH_ID, LOCATION_ID)
VALUES
('A58',TO_DATE('12/15/2011','MM/DD/YYYY'),123,'ABC','C3');

INSERT INTO DISCOVERY
(DISC_ID, DISC_DATE, DINO_ID, ARCH_ID, LOCATION_ID)
VALUES
('R47',TO_DATE('07/18/2012','MM/DD/YYYY'),345,'MNO','A1');

INSERT INTO DISCOVERY
(DISC_ID, DISC_DATE, DINO_ID, ARCH_ID, LOCATION_ID)
VALUES
('F21',TO_DATE('06/15/2009','MM/DD/YYYY'),456,'JKL','E5');

INSERT INTO DISCOVERY
(DISC_ID, DISC_DATE, DINO_ID, ARCH_ID, LOCATION_ID)
VALUES
('B65',TO_DATE('05/10/2011','MM/DD/YYYY'),456,'ABC','F6');

INSERT INTO DISCOVERY
(DISC_ID, DISC_DATE, DINO_ID, ARCH_ID, LOCATION_ID)
VALUES
('O99',TO_DATE('08/20/2012','MM/DD/YYYY'),234,'MNO','G7');

INSERT INTO DISCOVERY
(DISC_ID, DISC_DATE, DINO_ID, ARCH_ID, LOCATION_ID)
VALUES
('H71',TO_DATE('05/10/2012','MM/DD/YYYY'),567,'ABC','F6');

INSERT INTO DISCOVERY
(DISC_ID, DISC_DATE, DINO_ID, ARCH_ID, LOCATION_ID)
VALUES
('B34',TO_DATE('07/25/2010','MM/DD/YYYY'),123,'DEF','D4');

INSERT INTO DISCOVERY
(DISC_ID, DISC_DATE, DINO_ID, ARCH_ID, LOCATION_ID)
VALUES
('K81',TO_DATE('08/01/2016','MM/DD/YYYY'),567,'MNO','B2');

我认为没有必要使用外部连接来满足问题的要求。他们要求的唯一字段是名字、姓氏和计数。。。。不需要输出恐龙的名称或位置，这意味着您可以使用下面的列表来获取所需的列表

SELECT ARC.FIRST_NAME, ARC.LAST_NAME, (select count(distinct loc.LOCATION_ID) 
                                                      from DISCOVERY dis
                                                      inner join LOCATION loc on dis.location_id = loc.location_id
                                                      inner join DINOSAUR din on din.DINO_ID = dis.DINO_ID
                                                      where ARC.ARCH_ID = dis.ARCH_ID
                                                      and DIS.DINO_ID = 123) as loc_disc_TREX
FROM ARCHEOLOGIST ARC;

SELECT ARC.FIRST_NAME, ARC.LAST_NAME, (select count(distinct loc.LOCATION_ID) 
                                                      from DISCOVERY dis
                                                      inner join LOCATION loc on dis.location_id = loc.location_id
                                                      inner join DINOSAUR din on din.DINO_ID = dis.DINO_ID
                                                      where ARC.ARCH_ID = dis.ARCH_ID
                                                      and DIS.DINO_ID = 123) as loc_disc_TREX
FROM ARCHEOLOGIST ARC;

我建议这样做：

SELECT a.first_name, a.last_name,
       COUNT(DISTINCT ds.location_id) AS locations_with_t_rex_found
  FROM archeologist a
  LEFT OUTER JOIN discovery ds
    ON ds.arch_id = a.arch_id
   AND ds.dino_id = 123
 GROUP BY a.first_name, a.last_name
 ORDER BY locations_with_t_rex_found DESC, a.first_name, a.last_name

这导致：

FIRST_NAME | LAST_NAME | LOCATIONS|u与_T_REX|u找到
-----------+-----------+---------------------------
欧内斯特|海明威| 2
艾恩兰德1
弗雷德|阿斯泰尔| 0
金吉尔|罗杰斯| 0
葛丽塔|嘉宝| 0

看看这个，看看它在起作用。（我已经调整了您的样本数据，因为您似乎在插入中将所有恐龙条目命名为“霸王龙”，而之前您发布了更为多样化的内容。）

与问题中的原始查询相比，关键区别（除了跳过一些表外）在于在左侧连接匹配条件中指定恐龙物种过滤条件，而不是在整体

WHERE

子句中（仅限制连接表，而不是整个结果）

与from相比，这种方法还允许您轻松获取其他“统计信息”，例如，要返回实际发现的计数（例如，要覆盖一个位置的多个发现），您只需将计数（ds.disc_id）添加到列表达式列表中即可

至于跳过表格：
您不需要引用

位置

表，因为您不需要位置名称，可以根据

发现

表中的

位置ID

计算不同的位置计数。您也不需要查询中的

恐龙

表，除非您希望根据恐龙名称而不是恐龙ID筛选T-Rex。要重新添加表，您需要注意如何加入。这应该起作用：

SELECT a.first_name, a.last_name,
       COUNT(DISTINCT ds.location_id) AS locations_with_t_rex_found
  FROM archeologist a
  LEFT OUTER JOIN (discovery ds
             INNER JOIN dinosaur dn ON ds.dino_id = dn.dino_id)
    ON ds.arch_id = a.arch_id
   AND dn.dino_name = 'Tyrannosaurus Rex'
 GROUP BY a.first_name, a.last_name
 ORDER BY locations_with_t_rex_found DESC, a.first_name, a.last_name