######web framework ########Flask ########Tornado

#########sql健忘 select a.username, b.* from user a Inner Join text b ON a.userid = b.userid;

EXTRACT

ROLLUP

####where语句不能放聚集函数 SELECT product_cd, SUM(a) x from account where status = 'ACTIVE' GROUP BY product_cd HAVING SUM(a) >= 100;

###子查询， 连接， 事务， 视图， 元数据

#####子查询 避免子查询 NOT IN (x,y,NULL)情况， 产生未知结果

=any 与 in等效

关联子查询，非关联子查询

if-condition Logic SEARCH-class:

CASE WHEN C1 THEN E1 WHEN C2 THEN E2 END

SELECT c.a CASE WHEN c.x = 'a' THEN CONCAT(i.aa,i.bb) WHEN c.x = 'b' THEN c.name FROM zzz c LEFT OUTER JOIN xxx i ON .....;

索引，视图，元数据 ...