sql中多表查詢及其左連字段

SELECT s.*,t.teach_name FROM `stu` s, `teacher` t WHERE s.teacher_id = t.row_id AND s.teacher_id = 1

s.*    s表中 所有字段   

t.teach_name    t表中teach_name 字段

SELECT s.*,t.teach_name  將查出s表中 所有字段與t表中teach_name 字段 拼接起來

`stu` s, `teacher` t   等於  `stu` AS s,` teacher` AS t    將stu表簡化命名爲s,將teacher表簡化命名爲t

左連字段
SELECT s.* ,t.teacher_name FROM `stu` AS s LEFT JOIN `teacher` AS t ON s.teacher_id = t.row_id WHERE s.teacher_id = 1

s.* ,t.teacher_name  只展現s表中所有字段加t表中teacher_name  字段

LEFT JOIN `teacher` AS t ON s.teacher_id = t.row_id 左連加上從teacher表中數據 對應爲s.teacher_id = t.row_id的字段進行篩選