| | 连接符
如果sql_mode开启开启了PIPES_AS_CONCAT，"||"视为字符串的连接操作符而非或运算符，和字符串的拼接函数Concat相类似，这和Oracle数据库使用方法一样的
select Region || ' ' || Name from city where Region = 'north';
GROUP BY
对GROUP BY后面的栏位的查询结果进行汇总分组，通常是结合聚合函数一起使用的
GROUP BY 有一个原则，就是 SELECT 后面的所有列中，没有使用聚合函数的列，必须出现在GEOUP EY后面。
语法:SELECT “栏位1”，SUM(“栏位2”) FROM “表名” GROUP BY “栏位1”;
select Store_Name,sum(Sales) from tickets group by Store_Name;
select Store_Name,sum(Sales) from tickets group by Store_Name order by Sales desc;
HAVING
用来过滤由GROUP BY语句返回的记录集，通常与GROUP BY语句联合使用
HAVING语句的存在弥补了WHERE关键字不能与聚合函数联合使用的不足。如果被SELECT的只有函数栏，那就不需要GROUP BY子句。
语法:SELECT “栏位1”，SUM(“栏位2”) FROM “表格名” GROUP BY “栏位1” HAVING(函数条件);
select Store_Name,sum(Sales) from tickets group by Store_Name having sum(Sales) >1000;
别名
栏位别名 表格别名
语法:SELECT “表格别名”.“栏位1” [AS] “栏位别名” FROM “表格名” [AS] “表格别名”;
select T.Store_Name as N,Date as D from tickets as T group by N;
select T.Store_Name as N,sum(Sales),Date as D from tickets as T group by N;
子查询
连接表格，在 WHERE 子句或 HAVI