Category: JS

Method 1: distinct select count(distinct CName) from Course   Method two: Using grouping group by select count(1) from Course group by CName  

Introduction to database 1concept 3 relational database in Song Dynasty (pure theory)   Relational database is the use of Microsoft Corp)   noSQL   MangoDB,Redis 5sqlbrief introduction   Structure  Query  Language >: client partmysql.exe” document, the operating environment iscmd > port number-u localhost” means the machine.  127.0.0.1” means the machine. If it is the machine, it can be omitted. -P default, it can be omitted. -u >root DB DataBase ( corresponds to the form in reality.) Record >. > Library option. explains: > is used to set the stored character...

This section focuses on: How to find out the relationship between two tables Three relations of tables   1. Introduction Because of the constraint of foreign key, the two tables form three relationships: Multi to one Multiple to many One-on-one Two, focus on understanding if you find out the relationship between the two tables.   Three, three relationships of tables （1）Books and publishers 　　One to many (or many to one): a publishing house can publish many books. Look at the picture and talk. 　　Association mode: foreign key     create table press( id int primary k...