tailieunhanh - Lecture Database management systems - Chapter 8: SQL

Lecture Database management systems - Chapter 8: SQL. SQL commands can be classified in to three types: Data Definition Language commands (DDL), Data Manipulation Language commands (DML), Data Control Language commands (DCL). | SQL 7/11/2011 1 Introduction SQL commands can be classified in to three types: Data Definition Language commands (DDL) Data Manipulation Language commands (DML) Data Control Language commands (DCL) 7/11/2011 2 Domain types Numeric: int. Integer (a finite subset of the integers that is machine-dependent). smallint. Small integer (a machine-dependent subset of the integer domain type). numeric(p,d). Fixed point number, with userspecified precision of p digits, with n digits to the right of decimal point. real, double precision. Floating point and doubleprecision floating point numbers, with machinedependent precision. float(n). Floating point number, with user-specified precision of at least n digits. 7/11/2011 3 Domain types String: char(n). Fixed length character string, with user-specified length n. varchar(n). Variable length character strings, with user-specified maximum length n nvarchar(n). similar to varchar, except it uses Unicode and therefore doubles the amount of space required to store the data. Text: holds data that is longer than 8,000 characters 7/11/2011 4 Domain types Datetime: datetime. store not only a date, but also a time alongside it. .