左连接（Left Join）查询
创建学生（student）表
CREATE TABLE student (
id int,
name varchar(20));
创建成绩（SC）表
CREATE TABLE SC (
id int,
grand char(10));
插入测试数据
INSERT INTO student VALUES (1, "Daniel");
INSERT INTO student VALUES (2, "Sean");
INSERT INTO student VALUES (3, "Leo");
INSERT INTO student VALUES (4, "Lisa");
INSERT INTO SC VALUES(1, "A");
INSERT INTO SC VALUES(3, "B");
INSERT INTO SC VALUES(4, "B");
左连接查询
SELECT name,grand
FROM student
LEFT JOIN SC ON student.id=SC.id AND SC.id <2
WHERE student.id >0;
To be continue....
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