SQL 聚合函数

SQL 聚合函数

SQL基本函数，聚合函数对一组值执行计算，并返回单个值，也被称为组函数。 聚合函数经常与 SELECT 语句的 GROUP BY 子句的HAVING一同使用。

函数名	函数功能
COUNT	结果的计数
AVG	结果的平均值
MAX	结果的最大值
MIN	结果的最小值
SUM	结果的总和

COUNT

SELECT COUNT(age) FROM `user_t`

AVG

SELECT AVG(age) FROM `user_t`

MAX

SELECT MAX(age) FROM `user_t`

MIN

SELECT MIN(age) FROM `user_t`

SUM

SELECT SUM(age) FROM `user_t`

附件

创建表结构和数据

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
-- Table structure for user_t
-- ----------------------------
DROP TABLE IF EXISTS `user_t`;
CREATE TABLE `user_t`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `user_name` varchar(30) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL,
  `password` varchar(10) CHARACTER SET gbk COLLATE gbk_chinese_ci NOT NULL,
  `age` int(11) NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE,
  UNIQUE INDEX `uk_uname`(`user_name`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 4 CHARACTER SET = gbk COLLATE = gbk_chinese_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of user_t
-- ----------------------------
INSERT INTO `user_t` VALUES (1, 'zhangsan', '123456', 21);
INSERT INTO `user_t` VALUES (2, 'lisi', '111111', 23);
INSERT INTO `user_t` VALUES (3, '赵柳', '222222', 19);

SET FOREIGN_KEY_CHECKS = 1;