PostgreSQL：动态创建结果列
我想在 PostgreSQL 查询中“动态”创建结果列。我有这些表：
CREATE SEQUENCE users_id;
CREATE TABLE users (
id INT PRIMARY KEY NOT NULL DEFAULT NEXTVAL('users_id'),
name VARCHAR(128) NOT NULL
);
CREATE SEQUENCE quota_rules_id;
CREATE TABLE quota_rules (
id INT PRIMARY KEY NOT NULL DEFAULT NEXTVAL('quota_rules_id'),
user_id INT REFERENCES users(id),
rule VARCHAR(255) NOT NULL
);
CREATE INDEX user_id_index ON quota_rules(user_id);
INSERT INTO users (name) VALUES ('myname'); -- id=1
INSERT INTO quota_rules (user_id, rule) VALUES (1, 'a');
INSERT INTO quota_rules (user_id, rule) VALUES (1, 'b');
INSERT INTO quota_rules (user_id, rule) VALUES (1, 'c');
并且想要一个返回此（1 行）的查询：
SELECT ............ user_id = 1;
name | quota_rule | quota_rule2 | quota_rule3
myname | a | b | c
I want to "dynamically" create the result columns in a PostgreSQL query. I have these tables:
CREATE SEQUENCE users_id;
CREATE TABLE users (
id INT PRIMARY KEY NOT NULL DEFAULT NEXTVAL('users_id'),
name VARCHAR(128) NOT NULL
);
CREATE SEQUENCE quota_rules_id;
CREATE TABLE quota_rules (
id INT PRIMARY KEY NOT NULL DEFAULT NEXTVAL('quota_rules_id'),
user_id INT REFERENCES users(id),
rule VARCHAR(255) NOT NULL
);
CREATE INDEX user_id_index ON quota_rules(user_id);
INSERT INTO users (name) VALUES ('myname'); -- id=1
INSERT INTO quota_rules (user_id, rule) VALUES (1, 'a');
INSERT INTO quota_rules (user_id, rule) VALUES (1, 'b');
INSERT INTO quota_rules (user_id, rule) VALUES (1, 'c');
And want a query that returns this (1 row):
SELECT ............ user_id = 1;
name | quota_rule | quota_rule2 | quota_rule3
myname | a | b | c
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查看 tablefunc 的
crosstab函数模块Check out the
crosstabfunction of the tablefunc module