一.group by 子句 group by 字句可对数据进行分组. 以MySQL5.5的sakila数据库中的film数据表举例:查找出各个电影等级的电影总数 mysql>SELECT rating, COUNT(*) AS ratingCount FROM film > GROUP BY rating 结果如下: 可以看出,group by 子句对其后接的字段进行了分组,而这里也用了聚集函数count()对各分组中的项目数进行统计. 二.聚集函数 由上例可以知道,聚集函数是对某个分组的所有
整理了日常用到的一些sqls 1.插入表 insert into table_B select * from table_A 2.清空表 truncate table test #清空表,结构还存在delete table test where ... #删除表中特定的数据drop table test #删除整表,包括结构 3. 导出到文件 select * from table_A where filed1 like '8422%' into outfile '/usr/local/mysq
Coursera课程<Using Databases with Python> 密歇根大学 Week3 Data Models and Relational SQL 15.4 Designing a Data Model 主要介绍了数据模型的重要性,以及数据模型构建的一些思考过程. 15.5 Representing a Data Model in Tables 概念模型 主键(Primary key),指的是一个列或多列的组合,其值能唯一地标识表中的每一行,通过它可强制表的实体完整性.主键主
Rating Time Limit:5000MS Memory Limit:32768KB 64bit IO Format:%I64d & %I64u Submit Status Practice HDU 4870 Description A little girl loves programming competition very much. Recently, she has found a new kind of programming competition named
Rating Time Limit: 10000/5000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)Total Submission(s): 578 Accepted Submission(s): 363Special Judge Problem Description A little girl loves programming competition very much. Recently, she h
Time Limit: 10000/5000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)Total Submission(s): 786 Accepted Submission(s): 496Special Judge Problem Description A little girl loves programming competition very much. Recently, she has fou
Problem Description A little girl loves programming competition very much. Recently, she has found a new kind of programming competition named "TopTopTopCoder". Every user who has registered in "TopTopTopCoder" system will have a ratin
Rating Time Limit: 10000/5000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others) Total Submission(s): 714 Accepted Submission(s): 452 Special Judge Problem Description A little girl loves programming competition very much. Recently, she