读书笔记：Sams Teach Yourself Microsoft® SQL Server T-SQL in 10 Minutes

• what is database：a simple metaphor, a database is a container, such as file cabinet,  which stores data in an organized way.
• caution: database is not database software which is called database management system (DBMS). people use dbms to manipulate database.
• table: all data in cabinet are recorded in tables, which is a structured list of data of a specific type.
• schema: information about database and table layout and properties.
• column = field = 字段 ＝ 列
• row = record = 记录 ＝ 行
• about key: no two rows in a table have same primary key value; every row must have a primary key, and the primary key can not be NULL.
• 主键可以有一个，也可以多个。
• do not update values of primary key
• do not reuse values of primary key
• SQL is a universal language to manipulate DBMS, but in fact, there is no DBMS verdors use the identical SQL.
• SQL Server提供180天的试用版，SQL Express版是免费的，我们还有什么使用盗版的理由？
• use：使用数据库；
• sp_databases：列出可用数据库；
• sp_tables：列出当前数据库中所有表；
• sp_tables null, dbo, database_name, "'table'"：只列出table，而非view，或system table
• sp_columns table_name：列出表解构
• identity是什么：系统自动生成的id
• sp_server_info：显示当前server信息
• sp_spaceused：显示已用空间