查找具有某种类型的多个关系的实体

Question

鉴于此 Postgres 模式：

DROP TABLE IF EXISTS asset_category;
DROP TABLE IF EXISTS asset;
DROP TABLE IF EXISTS category;


CREATE TABLE asset (
    "id" BIGINT NULL DEFAULT NULL,
    "name" TEXT NULL DEFAULT NULL,
    PRIMARY KEY ("id")
);
CREATE INDEX IF NOT EXISTS "IDX_id" ON asset (id);

CREATE TABLE category (
    "id" BIGINT NULL DEFAULT NULL,
    "type" TEXT NULL DEFAULT NULL,
    "name" TEXT NULL DEFAULT NULL,
    PRIMARY KEY ("id")
);
CREATE INDEX IF NOT EXISTS "IDX_id" ON category (id);

CREATE TABLE asset_category (
    "asset_id" BIGINT NULL DEFAULT NULL,
    "category_id" BIGINT NULL DEFAULT NULL,
    CONSTRAINT "FK_asset_id" FOREIGN KEY ("asset_id") REFERENCES "asset" ("id") ON UPDATE CASCADE ON DELETE SET NULL,
    CONSTRAINT "FK_category_id" FOREIGN KEY ("category_id") REFERENCES "category" ("id") ON UPDATE CASCADE ON DELETE SET NULL,
    UNIQUE (asset_id, category_id)
);

和一些演示数据

INSERT INTO asset (id, "name") VALUES(1, 'Awesome Asset');
INSERT INTO asset (id, "name") VALUES(2, 'Great Asset');
INSERT INTO asset (id, "name") VALUES(3, 'Super Asset');
INSERT INTO asset (id, "name") VALUES(4, 'Best Asset');
INSERT INTO asset (id, "name") VALUES(5, 'Hilarious Asset');

INSERT INTO category (id, "name", "type") VALUES(1, 'Awesome Category', NULL);
INSERT INTO category (id, "name", "type") VALUES(2, 'Great Category', 'folder');
INSERT INTO category (id, "name", "type") VALUES(3, 'Super Category', 'folder');
INSERT INTO category (id, "name", "type") VALUES(4, 'Best Category', NULL);
INSERT INTO category (id, "name", "type") VALUES(5, 'Hilarious Category', NULL);

INSERT INTO asset_category ("asset_id", "category_id") VALUES(1, 1);
INSERT INTO asset_category ("asset_id", "category_id") VALUES(1, 2);
INSERT INTO asset_category ("asset_id", "category_id") VALUES(2, 3);
INSERT INTO asset_category ("asset_id", "category_id") VALUES(2, 4);
INSERT INTO asset_category ("asset_id", "category_id") VALUES(3, 1);
INSERT INTO asset_category ("asset_id", "category_id") VALUES(3, 2);
INSERT INTO asset_category ("asset_id", "category_id") VALUES(3, 3);
INSERT INTO asset_category ("asset_id", "category_id") VALUES(4, 5);
INSERT INTO asset_category ("asset_id", "category_id") VALUES(5, 1);
INSERT INTO asset_category ("asset_id", "category_id") VALUES(5, 2);
INSERT INTO asset_category ("asset_id", "category_id") VALUES(5, 3);

我如何创建一个 SQL 查询来返回所有资产，这些资产具有多个关联的 folder 类型类别？

在这里我们可以看到，情况是这样的：

SELECT *
FROM asset a

LEFT JOIN asset_category ac ON a.id = ac.asset_id
LEFT JOIN category c ON c.id = ac.category_id AND c.type = 'folder'

WHERE c.id IS NOT NULL 

资产3和5有不止一个。

我如何识别那些有查询的人？

Answer 1

我想我有

SELECT a.id, a.name
FROM asset a
JOIN (
  SELECT asset_id
  FROM asset_category ac
  JOIN category c ON ac.category_id = c.id
  WHERE c.type = 'folder'
  GROUP BY asset_id
  HAVING COUNT(*) > 1
) sub ON a.id = sub.asset_id;