W 3 School Learning Database

W3 School Learning Database address:

Http://www.jb51.net/w3school/sql/sql_select.htm

One, SQL syntax

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 for executing queries. However, the SQL language also contains syntax for updating, inserting, and deleting records.

The query and update Directives form the DML portion of SQL:

• SELECT -get data from a database table
• Update-updating data in a database table
• Delete-deletes data from the database table
• INSERT INTO-inserts data into a database table

The Data definition language (DDL) portion of SQL gives us the ability to create or delete tables. We can also define indexes (keys), specify links between tables, and impose constraints between tables.

The most important DDL statement in SQL:

• CREATE database-creating new databases
• alter database-Modify Databases
• CREATE TABLE-Creates a new table
• ALTER TABLE -Change (change) database table
• Drop Table-delete tables
• CREATE index-Creating indexes (search key)
• Drop Index-delete indexes

W 3 School Learning Database