MySql 单表查询练习

学生表students

建表语句：  CREATE TABLE `students`  (   `name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '姓名',   `age` int(11) NULL DEFAULT NULL COMMENT '年龄',   `gender` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT 'M=男, F=女' ) ENGINE = InnoDB CHARACTER SET = utf8; -- 学生表数据： INSERT INTO `students` VALUES ('张一', 12, '男'); INSERT INTO `students` VALUES ('张二', 18, '男'); INSERT INTO `students` VALUES ('张二', 19, '男'); INSERT INTO `students` VALUES ('张三', 122, '男'); INSERT INTO `students` VALUES ('张四', 123, '男'); INSERT INTO `students` VALUES ('张五', 161, '男'); INSERT INTO `students` VALUES ('张六', 66, '男'); INSERT INTO `students` VALUES ('张七', 35, '女'); INSERT INTO `students` VALUES ('张八', 55, '男'); INSERT INTO `students` VALUES ('张九', 56, '男'); INSERT INTO `students` VALUES ('张十', 96, '男'); INSERT INTO `students` VALUES ('张十一', 11, '男');

单表基础查询

1)查询表中所有数据 SELECT * FROM students 2)显示students表中的NAME和age列 SELECT `name`,age FROM students; 3)相同的名字只显示一次 SELECT * FROM students GROUP BY `name` 4)查询表中年龄小于16岁的数据 SELECT * FROM students WHERE age < 16 5) 查询年龄大于18岁的数据, 并按倒序排列 SELECT * FROM students WHERE  age > 18 ORDER BY age DESC 6)查询年龄在18-30之间的数据(包括18, 30) SELECT * FROM students  WHERE  age BETWEEN 18 AND 30   #  查询年龄在18-30之间的数据(不包括18, 30) SELECT * FROM students  WHERE  age >18  AND age <30 7)查询所有年龄不是66岁的数据 SELECT * FROM  students WHERE age !=66 8)查询所有姓名包括”一”的数据 SELECT * FROM students WHERE `name` LIKE  '%一%'  9)统计表中男, 女的数量分别是多少 SELECT gender 性别,COUNT(*) 数量 FROM students  GROUP BY gender    10)查询表中所有数据平均年龄 SELECT  AVG(age) 平均年龄 FROM  students   11)查询最大年龄 SELECT MAX(age) FROM students   # 延伸 查询最大年龄的所有信息 SELECT  *  FROM students   WHERE   age=(SELECT MAX(age) FROM  students) # 查询最小年龄  SELECT MIN(age) FROM students

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