- COUNT():总行数
- MAX():最大值
- MIN():最小值
- SUM():求和
- AVG():平均值
SELECT COUNT(*) FROM heros WHERE hp_max > 6000;
SELECT COUNT(role_assist) FROM heros WHERE hp_max > 6000;
-- COUNT(*)只统计数据行数,不管某个字段是否为NULL.
-- COUNT(role_assist)会忽略为NULL的数据行.
SELECT MAX(hp_max) FROM heros WHERE role_main = '射手' or role_assist = '射手';
SELECT COUNT(*), AVG(hp_max), MAX(mp_max), MIN(attack_max), SUM(defense_max) FROM heros WHERE role_main = '射手' or role_assist = '射手';
-- AVG,MAX,MIN等聚集函数会自动忽略值为NULL的数据行,MAX和MIN函数月可以用于字符串类型数据的统计,如果是英文字母,则按照A-Z的顺序排列,越往后,数值越大.
-- 如果是汉字则按照全拼拼音进行排列.
SELECT MIN(CONVERT(name USING gbk)), MAX(CONVERT(name USING gbk)) FROM heros;
SELECT COUNT(DISTINCT hp_max) FROM heros;
SELECT ROUND(AVG(DISTINCT hp_max), 2) FROM heros;