【课堂笔记】【SQL】9.Using DDL Statements to Create and Manage Tables

5dm

  Database Objects 包括：

TABLE,VIEW,SEQUENCE,INDEX,SYNONYM

 

Data Types

Data Type	Description
VARCHAR2(size)	Variable-length character data
CHAR(size)	Fixed-length character data
NUMBER(p,s)	Variable-length numeric data
DATE	Date and time values
LONG	Variable-length character data (up to 2 GB)
CLOB	Character data (up to 4 GB)
RAW and LONG RAW	Raw binary data
BLOB	Binary data (up to 4 GB)
BFILE	Binary data stored in an external file (up to 4 GB)
ROWID	A base-64 number system representing the unique address of a row in its table

 

 

5dm

Datetime Data Types 

Data Type	Description
TIMESTAMP	Date with fractional seconds含微秒
INTERVAL YEAR TO MONTH	Stored as an interval of yearsand months记录两个时间的时间年月间隔
INTERVAL DAY TO SECOND	Stored as an interval of days, hours, minutes, and seconds记录两个时间的时间天秒间隔

Constraints包括：

–NOT NULL

–UNIQUE

–PRIMARY KEY

–FOREIGN KEY

–CHECK

约束名默认为：SYS_Cn……