Data Organization, SQL Server, Interview Preparation Notes

2019年12月15日 7708点热度 0人点赞 3条评论

内容目录

Categories of Knowledge Points to Master in T-SQL

SQL for executing queries against databases
SQL for retrieving data from databases
SQL for inserting new records into databases
SQL for updating data within databases
SQL for deleting records from databases
SQL for creating new databases
SQL for creating new tables in databases
SQL for creating stored procedures in databases
SQL for creating views in databases
SQL for setting permissions on tables, stored procedures, and views

SQL is an ANSI standard computer language used to access and manipulate database systems. SQL statements are used to retrieve and update data within databases. SQL can work in conjunction with database programs such as MS Access, DB2, Informix, MS SQL Server, Oracle, Sybase, and other database systems.

Unfortunately, there are many different versions of SQL, but to remain compatible with the ANSI standard, they must support some key keywords (such as SELECT, UPDATE, DELETE, INSERT, WHERE, etc.) in similar ways.

Reference: http://www.w3school.com.cn/sql/sql_intro.asp

SQL DML and DDL

SQL can be divided into two parts: Data Manipulation Language (DML) and Data Definition Language (DDL).

SQL (Structured Query Language) is the syntax used for executing queries. However, SQL also contains syntax for updating, inserting, and deleting records.

The query and update commands make up the DML part of SQL:

Summary: Select, Update, Delete, Insert

SELECT - retrieve data from database tables
UPDATE - update data in database tables
DELETE - remove data from database tables
INSERT INTO - insert data into database tables

The Data Definition Language (DDL) part of SQL enables us to create or delete tables. We can also define indexes (keys), specify relationships between tables, and enforce constraints between tables.

The most important DDL statements in SQL: