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Overview of Tables (154)

原创 网络安全 作者:tsinglee 时间:2007-11-07 11:26:53 0 删除 编辑

Tables are the basic unit of data storage in an Oracle database. Data is stored in rows
and columns. You define a table with a table name (such as employees) and set of
columns. You give each column a column name (such as employee_id, last_name,
and job_id), a datatype (such as VARCHAR2, DATE, or NUMBER), and a width. The
width can be predetermined by the datatype, as in DATE. If columns are of the NUMBER
datatype, define precision and scale instead of width. A row is a collection of column
information corresponding to a single record.
You can specify rules for each column of a table. These rules are called integrity
constraints. One example is a NOT NULL integrity constraint. This constraint forces the
column to contain a value in every row.
You can also specify table columns for which data is encrypted before being stored in
the datafile. Encryption prevents users from circumventing database access control
mechanisms by looking inside datafiles directly with operating system tools.
After you create a table, insert rows of data using SQL statements. Table data can then
be queried, deleted, or updated using SQL.

1. 表是 Oracle 数据库中最基本的数据存储结构 . 数据在表中以行和列的形式存储.
2. 定义表时指定表名 , 列名 , 数据类型
3. 用户可以为表列设定规则 , 称为完整性约束.


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