我如何旋转 PostgreSQL table？

Question

我有 table company_representatives 看起来像这样：

创建table脚本：

CREATE TABLE IF NOT EXISTS company_representatives (
 _id          integer NOT NULL,
 name         varchar(50) NOT NULL,
 surname      varchar(100) NOT NULL,
 date_of_join date NOT NULL,
 role         varchar(250) NOT NULL,
 company_id   integer NOT NULL,
 CONSTRAINT PK_company_representatives PRIMARY KEY ( _id ),
 CONSTRAINT FK_144 FOREIGN KEY ( company_id ) REFERENCES companies ( _id )
);

INSERT INTO company_representatives VALUES
(1,'random name','random surname', '2001-01-23', 'CEO', 1),
(2,'next random name','next random surname', '2001-01-23', 'Co-founder', 1),
(3,'John','Doe', '2003-02-12', 'HR', 1),
(4,'Bread','Pitt', '2001-01-23', 'Security officer', 1),
(5,'Toast','Malone', '1997-11-05', 'CEO', 2),
...

我需要调整此 table 使其列看起来像这样：

company_id | CEO | Co-Founder | HR | Security Officer
    1         1         2       3            4          "_id of company's representatives"
    2         5         6       7            8
    3         9        10       11          12

Answer 1

您可以直接在 SELECT 子句中直接使用 FILTER：

SELECT DISTINCT ON (company_id)
  company_id,
  count(*) FILTER (WHERE role = 'CEO') AS CEO,
  count(*) FILTER (WHERE role = 'Co-founder') AS "Co-Founder",
  count(*) FILTER (WHERE role = 'HR') AS HR,
  count(*) FILTER (WHERE role = 'Security officer') AS "Security Officer"
FROM company_representatives
GROUP BY company_id;

有问题的是，角色所附加的值的实际含义尚不清楚，所以我假设您只是想计算它们。如果不行，换成其他聚合函数就好了。

编辑（见评论）：使用crosstab 透视table，假设所有公司的每个角色都有一个记录：

SELECT *
FROM crosstab(
 'SELECT company_id,  _id, name
  FROM company_representatives ORDER BY company_id,role' 
) AS ct(company_id integer,ceo text,co_founder text,hr text,security_officer text);

演示：db<>fiddle

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