Question

我创建了2个表：

表1：学生

id_student varchar5
student_name varchar [30]

表2：缺席

id_absent int [11]（pk）
id_student varchar [5]（fk）
date_absent [date]
info_absent varchar [15]

我今天要显示缺席，但我想要显示所有数据学生。

实施例

**name | info_absent**

ridwan | present

adesta | present

eko  | null 

desti | null

今天没有这个数据样本可能是eko或desti没有出现或生病。

当我这样查询时：

SELECT sw.student_name,ab.info_absent
    FROM student AS sw 
    left outer join absent AS ab  on
    sw.id_student=ab.id_student
     where ab.date_absent='now()'

这只显示数据

**name | info_absent**

ridwan | present

adesta | present

我希望eko和desti也会显示在这些数据中。

Answer 1

这是否正常工作？

SELECT sw.student_name, ab.info_absent FROM student sw 
LEFT JOIN absent ab ON ab.id_student = sw.id_student && ab.date_absent = NOW();

您也可以将info_absent中的NULL替换为您想要的任何内容：

SELECT sw.student_name, IFNULL(ab.info_absent, 'Seems present') FROM student sw 
LEFT JOIN absent ab ON ab.id_student = sw.id_student && ab.date_absent = NOW();

Answer 2

为什么不

SELECT sw.student_name,ab.info_absent
FROM student AS sw 
left outer join absent AS ab  on
sw.id_student=ab.id_student

查询SQL条件显示表1和表2中的所有数据

2 个答案: