PostgreSQL多条件语句 [英] PostgreSQL multiple criteria statement

问题描述

我有以下postgreSQL语句，用于返回学校开学和需要上学的日期

I have the following postgreSQL statement that returns dates that school is open and attendance needs to be taken

SELECT school_date 
FROM attendance_calendar 
WHERE syear='$syear' 
AND school_date<CURRENT_DATE 
AND calendar_id='$cal_ID'

然后，我有另一个表名为Attenance_completed，该表具有一列school_date，我希望从上述语句中查询每个返回的日期。但是，而不是做两个不同的语句，只是想知道是否有人可以帮助合并该语句？

I then have another table called attendance_completed which has a column called school_date that i want to query for each returned date from the above statement. But instead of doing two different statements, just wondering if someone can help combine the statement?

基本上，我希望以上语句检查返回的school_date是否存在于表称为Attence_completed，并且仅返回缺少的日期。

Basically, i would like the above statement to check if the returned school_date exists in the table called attendance_completed, and only return the dates that are missing.

谢谢

推荐答案

这应该为您工作：

SELECT cal.school_date
FROM attendance_calendar cal
WHERE  cal.school_date NOT IN (
    SELECT com.school_date
    FROM attendance_completed com
    WHERE com.school_date IS NOT NULL
) AND
cal.syear = '$syear' AND
cal.school_date < CURRENT_DATE AND
cal.calendar_id = '$cal_ID;

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