是否可以指定您想要在左连接表中的字段
。
SELECT * FROM students
LEFT OUTER JOIN classes_enrolled (can i specify fields here)
ON students.student_id = classes_enrolled.student_id
我只想从左连接表 classes_registry中获取字段subject,而不是让*匹配行的所有字段被附加
为什么不试试
SELECT students.* ,
classes_enrolled.subject
FROM students LEFT OUTER JOIN
classes_enrolled ON students.student_id = classes_enrolled.student_id
实际上,指定字段名比使用SELECT *
您可以选择以下任何一个:
使用子查询查询指定的列,
SELECT *
FROM students
LEFT OUTER JOIN
(
SELECT student_id, subject
FROM classes_enrolled
) b ON students.student_id = b.student_id
或者我更喜欢的——手动选择这些列,
SELECT students.*,
classes_enrolled.subject
FROM students
LEFT OUTER JOIN classes_enrolled
ON students.student_id = classes_enrolled.student_id
尝试如下SELECT, classes_enroll。主题,*来自学生,左外连接classes_enroll在学生。