DISTINCT() 过滤重复
COUNT() 统计个数
SELECT COUNT(DISTINCT(cateid)) FROM cs_goods ORDER BY cateid
SELECT COUNT(*) FROM cs_goods

SUM() 求和
求price列总和
SELECT SUM(price) FROM cs_goods
求每个月总销售额
SELECT SUM(price),SUBSTRING(FROM_UNIXTIME(createtime),1,7) AS ymonth FROM cs_goods GROUP BY ymonth;
求每天总销售额
SELECT SUM(price),DATE(FROM_UNIXTIME(createtime)) AS ymonth FROM cs_goods GROUP BY ymonth ORDER BY ymonth DESC;
求每天销售额大于100的记录
SELECT SUM(price) AS total,DATE(FROM_UNIXTIME(createtime)) AS ymonth FROM cs_goods GROUP BY ymonth HAVING total>100 ORDER BY ymonth DESC;

AVG() 求平均
求所有商品平均单价
SELECT AVG(price) FROM cs_goods;
求每个分类下商品平均单价
SELECT AVG(a.price),a.cateid,b.category FROM cs_goods a INNER JOIN cs_category b ON(a.cateid=b.id) GROUP BY cateid;
MAX() 求最大值
求每个分类下最高单价
SELECT MAX(a.price),a.cateid,b.category FROM cs_goods a INNER JOIN cs_category b ON(a.cateid=b.id) GROUP BY cateid;
MIX() 求最小值
求每个分类下最小单价
SELECT MIX(a.price),a.cateid,b.category FROM cs_goods a INNER JOIN cs_category b ON(a.cateid=b.id) GROUP BY cateid;

表的求和及计算