现创建表和初始化柱调沃数据：CREATE TABLE student ( student_id int (11) PRIMARY KEY NOT NULL AUTO_INCREMENT, student_name VARCHAR (20) CHARACTER SET utf8 NOT NULL, student_sex VARCHAR (2), student_age INTEGER (3), dept_id VARCHAR (2), class_id VARCHAR (8) 各板); CREATE TABLE course ( course_id int (11) PRIMARY KEY NOT NULL AUTO_INCREMENT, course_name VARCHAR (40) CHARACTER SET utf8 NOT NULL, course_hours INTEGER (2), course_credit FLOAT (1) ); create TABLE grade( grade_id int(11) PRIMARY KEY NOT NULL AUTO_INCREMENT, student_id INT(11) NOT NULL, course_id int(11) NOT NULL, grade_val DOUBLE);INSERT INTO student (student_name,student_sex,student_age) VALUES('Tom'晃夏,'M',18);INSERT INTO student (student_name,student_sex,student_age) VALUES('Jar','M',17);INSERT INTO student (student_name,student_sex,student_age) VALUES('Mary','G',18);INSERT INTO student (student_name,student_sex,student_age) VALUES('Tim','G',16);INSERT INTO student (student_name,student_sex,student_age) VALUES('Sala','G',18);INSERT INTO student (student_name,student_sex,student_age) VALUES('Miki','G',19);INSERT INTO student (student_name,student_sex,student_age) VALUES('Jack','M',18);INSERT INTO student (student_name,student_sex,student_age) VALUES('Sar','G',17);INSERT INTO student (student_name,student_sex,student_age) VALUES('Lide','G',18);INSERT INTO student (student_name,student_sex,student_age) VALUES('Bill','M',17);INSERT INTO course (course_name) VALUES('英语');INSERT INTO course (course_name) VALUES('语文');INSERT INTO course (course_name) VALUES('数学');INSERT INTO grade(student_id,course_id,grade_val) VALUES(1,1,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(2,1,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(3,1,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(4,1,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(5,1,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(6,1,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(7,1,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(8,1,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(9,1,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(10,1,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(1,2,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(2,2,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(3,2,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(4,2,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(5,2,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(6,2,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(7,2,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(8,2,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(9,2,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(10,2,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(1,3,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(2,3,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(3,3,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(4,3,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(5,3,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(6,3,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(7,3,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(8,3,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(9,3,80);INSERT INTO grade(student_id,course_id,grade_val) VALUES(10,3,80);
查询表的记录但不需要显示重复的记录，使用distinct，如图
对于多张表查询，同时满足条件两个或多个条件结合起来的记录需要使用and
如果查询的结果要求只要有一个成立就可以，可以使用OR,如图
把相同值分成一组，可以使用Group BY来实现，如图
如果需要对值进行排序，可以使用ORDER BY,如图