Question

I have two tables, let s call them table1 and table2. They both have a column called ID1 and ID2 which are respective PK for each of two tables.

我还有另一个表格,即:table3,其中载有ID1和ID2,在这两个表格之间建立了许多到许多关系。

我需要从<代码>表2上查阅所有与<代码>>>> <1中记录无关的记录。

Ex.

Table 1 contains a record with ID = 1
Table 2 contains two records with ID 1, 2
Table 3 contains one record with values 1 - 1

我需要问一下结果2。

谁能建议我走一条道路?

Thanks

Answer 1

SELECT t2.ID2
    FROM table2 t2
    WHERE NOT EXISTS(SELECT NULL
                         FROM table3 t3
                         WHERE t3.ID2 = t2.ID2);

也可以使用LEFT JOIN:

SELECT t2.ID2
    FROM table2 t2
        LEFT JOIN table3 t3
            ON t2.ID2 = t3.ID2
    WHERE t3.ID2 IS NULL;

友情链接