左连接语法：
    SELECT
    *
    FROM
    TableALEFT JOIN
    TableB
    `**ON **condition;<br />![image.png](https://cdn.nlark.com/yuque/0/2021/png/21689380/1622140335053-15af9a76-6779-40f3-9b42-fc62e9ed4780.png#align=left&display=inline&height=135&margin=%5Bobject%20Object%5D&name=image.png&originHeight=164&originWidth=665&size=33192&status=done&style=none&width=549)<br />例子：<br />SELECT<br /> *<br />FROM<br /> ykd_teacher<br /> LEFT JOIN ykd_course ON ykd_teacher.id = ykd_course.teacher_id;`
    image.png
    image.png
    image.png