帮助SQL MINUS语句

Question

我有3个表，Reporter_Vacation，Dropper，Vacation_Temp。

Reporter_Vacation有Reporter，Start_dt，End_dt（3个组合是唯一的）

Dropper有Dropper_ID和Reporter（两者都是唯一的）

Vacation_Temp有Dropper_ID，Start_dt，End_dt（3个组合是唯一的）

如何在Vacation_Temp中找到不在Reporter_Vacation中的Reporter，Start_dt和End_dt？

SELECT DROPPER_ID, BEGIN_DT, END_DT 
FROM VACATION_TEST
    MINUS 
SELECT DROPPER.DROPPER_ID, REPORTER_VACATION.BEGIN_DT, REPORTER_VACATION.END_DT 
FROM REPORTER_VACATION, DROPPER 
WHERE DROPPER.REPORTER = REPORTER_VACATION.REPORTER;

Answer 1

比MINUS更标准化，更可索引（因此通常更快）的替代方法是空连接。

使用LEFT JOIN引入您不想要的表，在表中没有值的地方留下NULL。然后在WHERE子句中测试该NULL。将其扩展为两个连接表：

SELECT vacation_test.dropper_id, vacation_test.begin_dt, vacation_test.end_dt
FROM vacation_test
    LEFT JOIN dropper ON
        dropper.dropper_id=vacation_test.dropper_id
    LEFT JOIN reporter_vacation ON
        reporter_vacation.dropper_id=dropper.dropper_id AND
        reporter_vacation.begin_dt=vacation_test.begin_dt AND
        reporter_vacation.end_dt=vacation_test.end_dt
WHERE reporter_vacation.begin_dt IS NULL