SELECT * FROM product;-- 查询所有列
SELECT pro_id,pro_name FROM product;-- 查询指定列
SELECT pro_name AS '产品名称',price FROM product;-- 添加常量列          把pro_id改为“产品名称”（添加常量列只是显示这个名称，查询后还是原来的）并查询
SELECT pro_id,(protype+price)AS'总价格' FROM product;-- 查询时合并列    protype+price两列相加合并添加常量列 注意：合并列只能合并数值类型的字段
SELECT DISTINCT protype FROM product;-- 查询时去除重复列
SELECT * FROM product WHERE pinpai='索尼'AND chandi='深圳';-- 条件查询   and(并且)     or(或者)
SELECT * FROM product WHERE protype>1;-- 比较查询                         >   <   >=  <=  =  <>(不等于)
SELECT * FROM product WHERE protype BETWEEN 1 AND 2;-- 查询protype在1和2之间的  (等价于>=1 并且 <=2)
SELECT * FROM product WHERE protype >=1 AND protype <=2;

SELECT * FROM product WHERE protype IS NULL;-- 查询protype是null的
SELECT * FROM product WHERE protype IS NOT NULL;-- 查询protype不是mull的SELECT * FROM product WHERE protype = '';-- 查询protype是空字符串的
SELECT * FROM product WHERE protype <> '';-- 查询protype不是空字符串的-- 查询product不为空的
SELECT * FROM product WHERE protype IS NOT NULL AND protype <> '';

SELECT * FROM product WHERE pro_name LIKE '%索尼%';

-- 查询protype的总销量
SELECT SUM(protype) FROM product;
-- 查询protype的销量的最大值
SELECT MAX(protype) FROM product;
-- 查询protype的销量的最小值
SELECT MIN(protype) FROM product;
-- 查询protype的销量的平均值
SELECT AVG(protype) FROM product;-- 查询product的列有几款产品
-- 注意：count（）函数统计的数量不包含null的数据
-- 使用count统计表的记录数，要使用不包含null值的字段
SELECT COUNT(*) FROM product;

-- 查询排序
SELECT * FROM product ORDER BY price ASC; -- 升序
SELECT * FROM product ORDER BY price;SELECT * FROM product ORDER BY price DESC; -- 倒序-- 查询表中销量是1的对价钱排序
SELECT * FROM product WHERE protype=1 ORDER BY price;-- 先排第一个，如果有相同的，相同的几个数据再按第二个排序
SELECT * FROM product ORDER BY protype DESC,price ASC;

-- 分组查询 protype1\2\3各是多少个
SELECT protype,COUNT(*) FROM product GROUP BY protype;
-- 查询protype中分组查询个数大于2的
SELECT protype,COUNT(*) FROM product GROUP BY protype HAVING COUNT(*)>2;