Question

我有多个包含样本数据的表格：

CREATE TABLE public.languages (
  "id" bigserial NOT NULL,
  PRIMARY KEY ("id")
);

CREATE TABLE public.goods (
    "id" bigserial NOT NULL,
    PRIMARY KEY ("id")
);

CREATE TABLE public.good_texts (
  goodid int8 NOT NULL,
  title varchar(250) NOT NULL,
  languageid int8 NOT NULL,
  PRIMARY KEY (goodid, languageid)
);

CREATE TABLE "public".filtervariants (
  id                        bigserial NOT NULL,
  PRIMARY KEY (id));

CREATE TABLE "public".filtervariant_good (
  filtervariantid int8 NOT NULL,
  goodid          int8 NOT NULL,
  PRIMARY KEY (goodid,
               filtervariantid));

INSERT INTO "public"."languages" VALUES ('1');

INSERT INTO "public"."goods" VALUES ('385');

INSERT INTO "public"."good_texts" VALUES ('385', 'Dell Inspiron 5559', '1');

INSERT INTO "public"."filtervariants" VALUES ('1');
INSERT INTO "public"."filtervariants" VALUES ('2');
INSERT INTO "public"."filtervariants" VALUES ('3');
INSERT INTO "public"."filtervariants" VALUES ('4');
INSERT INTO "public"."filtervariant_good" VALUES ('1', '385');
INSERT INTO "public"."filtervariant_good" VALUES ('3', '385');

此查询

SELECT
    gt.*, goods.*
FROM
    good_texts gt
JOIN goods ON goods. ID = gt.goodid
JOIN filtervariant_good ON goods.id = filtervariant_good.goodid
WHERE
    gt.languageid = 1

两次返回记录，我无法理解原因。每当我删除

JOIN filtervariant_good ON goods.id = filtervariant_good.goodid

行只返回一次记录

请解释此次加入有什么问题。如果我将此表与其他表（此处未显示）结合使用，则可以正常工作。

Answer 1

嗯，filtervariant_good中有两行，goodid等于385，这就是原因。我怀疑你不关心在该表中有多行，而你只关心该表中是否存在商品。如果我的猜测是正确的，那么您可以执行以下操作：

SELECT
    gt.*, goods.*
FROM
    good_texts gt
JOIN goods ON goods. ID = gt.goodid
WHERE
    gt.languageid = 1
    AND exists(SELECT FROM filtervariant_good WHERE goods.id = filtervariant_good.goodid)

这将仅返回filtervariant_good中存在的商品。

在Postgresql中加入时选择结果中的重复enries

1 个答案: