Question

我有以下代码。

CREATE TABLE "s"."t1"
(
    "c1" BigSerial PRIMARY KEY,
    "c2" BigInt NOT NULL
)
WITH (OIDS=FALSE);

INSERT INTO s.t1 (c2) VALUES (100);
INSERT INTO s.t1 (c2) VALUES (200);

CREATE TABLE "s"."t2"
(
    "c1" BigSerial PRIMARY KEY,
    "c2" BigInt NOT NULL,
    "c3" BigInt NOT NULL,
    CONSTRAINT "fk1" FOREIGN KEY (c2) REFERENCES s.t1 (c1) ON DELETE SET NULL ON UPDATE CASCADE
)
WITH (OIDS=FALSE);

INSERT INTO s.t2 (c2, c3) VALUES (1, 2000);
INSERT INTO s.t2 (c2, c3) VALUES (1, 3000);

SELECT t1.c1
FROM s.t1 t1 
WHERE t1.c1 NOT IN 
(SELECT DISTINCT t1.c1 FROM s.t1 t1
 INNER JOIN s.t2 AS t2 on t2.c2 = t1.c1);

输出为2。

我正在尝试查看t1（c1）的列，并检查c1中是否有任何不属于t2的值（{{1} }}）。

使用count或outer join有更好的方法吗？

Answer 1

使用except：

select c1 from t1
except
select c2 from t2;

Answer 2

此问题称为反连接模式，您可以尝试使用left join和is null检查，例如：

SELECT t1.c1
FROM s.t1 t1 
LEFT JOIN s.t2 t2 ON t2.c2 = t1.c1
WHERE t2.c2 IS NULL

SQLFiddle

检查一个值是否在另一个表的列中

2 个答案: