[英]Joining a table of properties as columns and values?
CREATE TABLE person_properties (
person_id INT,
key TEXT,
value TEXT,
PRIMARY KEY (person_id, key)
);
CREATE TABLE persons (
id SERIAL PRIMARY KEY
);
我已經做到了:
INSERT INTO persons DEFAULT_VALUES; -- suppose id is 1
INSERT INTO person_properties (person_id, key, value) VALUES (1, 'age', '30')
INSERT INTO person_properties (person_id, key, value) VALUES (1, 'weight', '20lb')
我想選擇person
s的age
和weight
為列,從值person_properties
(或NULL
,如果不存在的話)。 我怎樣才能做到這一點?
SELECT * FROM persons
LEFT OUTER JOIN person_properties p1 ON persons.person_id = p1.person_id AND p1.key = 'age'
LEFT OUTER JOIN person_properties p2 ON persons.person_id = p2.person_id AND p2.key = 'weight'
您的架構是錯誤的。
key
是保留鍵,並且唯一表中不能有2個主鍵。
CREATE TABLE person_properties (
person_id INT,
cle TEXT,
value TEXT,
PRIMARY KEY (person_id)
);
CREATE TABLE persons (
id SERIAL PRIMARY KEY
);
和
您不能擁有兩次相同的主鍵...
INSERT INTO person_properties (person_id, cle, value) VALUES (**1**, 'age', '30');
INSERT INTO person_properties (person_id, cle, value) VALUES (**1**, 'weight', '20lb');
如果必須有兩行具有相同的鍵,那就不好了。
我建議您重做//重新考慮您的架構。
編輯:
CREATE TABLE person_properties (
person_id INT NOT NULL AUTO_INCREMENT,
pkey VARCHAR(10),
value TEXT,
PRIMARY KEY (person_id, pkey)
);
CREATE TABLE persons (
id SERIAL PRIMARY KEY
);
INSERT INTO person_properties (pkey, value) VALUES ('age', '30');
INSERT INTO person_properties (pkey, value) VALUES ('weight', '20lb');
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