Character Data Types

字符数据类型

• Character data types store character (alphanumeric) data in strings.

字符数据类型存储在字符串中的字符 （字母或数字） 数据。

• The most commonly used character data type is VARCHAR2, which is the most efficient option for storing character data.

最常用的字符数据类型是 VARCHAR2，它是用于存储字符数据的最有效的选项。

• The byte values correspond to the character encoding scheme, generally called a character set or code page. The database character set is established at database creation.

与字符编码模式相对应的字节值，一般称为 字符集或 代码页。 数据库字符集是在数据库创建时建立的。

•  Examples of character sets are 7-bit ASCII, EBCDIC, and Unicode UTF-8.

字符集的例子有 7 位 ASCII 码、 EBCDIC码、和 Unicode utf-8。

• The length semantics of character data types can be measured in bytes or characters.

字符数据类型的长度语义可以以字节或字符为单位。

•  Byte semantics treat strings as a sequence of bytes. This is the default for character data types.

字节语义将字符串视为一个字节序列。 这是字符数据类型的默认值。

• Character semantics treat strings as a sequence of characters. A character is technically a code point of the database character set.

字符语义将字符串视为字符序列。 一个字符在技术上是数据库字符集的编码点。

VARCHAR2 、CHAR NCHAR、NVARCHAR2

Oracle Database compares VARCHAR2 values using nonpadded comparison semantics and compares CHAR values using blank-padded comparison semantics.

Oracle 数据库将使用非填充比较语义来比较 VARCHAR2 值，而使用空白填充比较语义来比较 CHAR 值。

Numeric Data Types

数字数据类型

• The Oracle Database numeric data types store fixed and floating-point numbers, zero, and infinity.

Oracle 数据库的数字数据类型存储固定和浮点数字、零、或无穷。

• Some numeric types also store values that are the undefined result of an operation, which is known as "not a number" or NAN.

某些数值类型也可以存储未定义操作的结果值，叫做"非数字"或 NAN。

• Oracle Database stores numeric data in variable-length format. Each value is stored in scientific notation, with 1 byte used to store the exponent.

Oracle 数据库以变长格式存储数字数据。用科学计数法存储值，其中一个字节用于存储指数。

• The database uses up to 20 bytes to store the mantissa, which is the part of a floating-point number that contains its significant digits.

数据库使用最多 20 个字节存储尾数，即浮点数的有效位数部分。

• Oracle Database does not store leading and trailing zeros.

Oracle 数据库不会存储前导零和结尾零。

NUMBER Data Type

• The NUMBER data type stores fixed and floating-point numbers.

NUMBER 数据类型存储固定和浮点数字。

• The database can store numbers of virtually any magnitude.

数据库可以存储几乎任何规模的数字。

• This data is guaranteed to be portable among different operating systems running Oracle Database.

此数据保证在运行 Oracle 数据库的不同操作系统之间可移植。

• The NUMBER data type is recommended for most cases in which you must store numeric data.

大多数情况下，当您必须存储数值数据时，推荐使用 NUMBER 数据类型。

• You specify a fixed-point number in the form NUMBER(p,s), where p and s refer to the following characteristics:

按 NUMBER(p,s)的形式定义定点数，p 和 s 有以下特征：

Floating-Point Numbers

• Oracle Database provides two numeric data types exclusively for floating-point numbers: BINARY_FLOAT and BINARY_DOUBLE.

Oracle 数据库为浮点数提供了两种互斥的数值数据类型： BINARY_FLOAT和 BINARY_DOUBLE。

• These types support all of the basic functionality provided by the NUMBER data type.

这两种类型支持所有 NUMBER 数据类型提供的基本功能。

• However, while NUMBER uses decimal precision, BINARY_FLOAT and BINARY_DOUBLE use binary precision, which enables faster arithmetic calculations and usually reduces storage requirements.

然而，相比 NUMBER使用十进制精度，BINARY_FLOAT 和BINARY_DOUBLE 使用二进制精度，可以使算术计算更快并且通常可以降低存储需求。

• BINARY_FLOAT and BINARY_DOUBLE are approximate numeric data types.

BINARY_FLOAT 和 BINARY_DOUBLE 是近似数字数据类型。

• They store approximate representations of decimal values, rather than exact representations.

它们存储十进制的值的近似表示，而不是精确的表示形式。

•  For example, the value 0.1 cannot be exactly represented by either BINARY_DOUBLE or BINARY_FLOAT.

例如值 0.1不能用BINARY_DOUBLE 或 BINARY_FLOAT 完全精确地表示。他们经常用于科学计算。

• They are frequently used for scientific computations. Their behavior is similar to the data types FLOAT and DOUBLE in Java and XMLSchema.

其行为类似于 Java 或 XMLSchema 中的 FLOAT 和 DOUBLE 数据类型。

Datetime Data Types

日期时间数据类型

Datetime Data Types

The datetime data types are DATE and TIMESTAMP. Oracle Database provides comprehensive time zone support for time stamps.

日期时间数据类型包括 DATE和 TIMESTAMP。Oracle 数据库为时间戳提供全面的时区支持。

Rowid Data Types

ROWI数据类型

Rowid Data Types

Every row stored in the database has an address. Oracle Database uses a ROWID data type to store the address (rowid) of every row in the database. Rowids fall into the following categories:

存储在数据库中的每一行都有一个地址。Oracle 数据库使用 ROWID 数据类型存储在数据库中的每一行的地址 (rowid)。Rowids 分为以下几类：

A data type called the universal rowid, or UROWID, supports all kinds of rowids.

有一种数据类型称为用 通用 rowid 或 UROWID，支持各种 rowids。

Use of Rowids

Oracle Database uses rowids internally for the construction of indexes.

Oracle 数据库在内部使用 rowids用于构造索引，

A B-tree index, which is the most common type, contains an ordered list of keys divided into ranges. Each key is associated with a rowid that points to the associated row‘s address for fast access.

最常见的 B 树索引，包含一个被划分成多个键范围的排序列表。每个键都与一个指向关联的行地址的rowid 相关联，用于快速访问。

End users and application developers can also use rowids for several important functions:

最终用户和应用程序开发人员也可以使用rowids 的几个重要功能：

• Rowids are the fastest means of accessing particular rows.

Rowids 是访问特定行的最快方式。

• Rowids provide the ability to see how a table is organized.

Rowids 提供了查看表的组织方式的能力。

• Rowids are unique identifiers for rows in a given table.

Rowids 是给定表中的行的唯一标识符。

You can also create tables with columns defined using the ROWID data type. For example, you can define an exception table with a column of data type ROWID to store the rowids of rows that violate integrity constraints. Columns defined using the ROWID data type behave like other table columns: values can be updated, and so on.

您也可以创建带 ROWID 数据类型列的表。例如，您可以定义一个异常表，其中一列为 ROWID 数据类型，以存储违反了完整性约束的行 rowids。使用ROWID 数据类型定义的列像其他表中的列一样， 其值可以更新，等等。

ROWID Pseudocolumn

• Every table in an Oracle database has a pseudocolumn named ROWID.

Oracle 数据库中的每个表都有一个名为 ROWID 的 伪列。

• A pseudocolumn behaves like a table column, but is not actually stored in the table.

伪列类似于表列，但实际上并不存储在表中。

• You can select from pseudocolumns, but you cannot insert, update, or delete their values.

您可以从伪列中选择数据，但不能插入、更新、或删除它们的值。

A pseudocolumn is also similar to a SQL function without arguments. Functions without arguments typically return the same value for every row in the result set, whereas pseudocolumns typically return a different value for each row.

• Values of the ROWID pseudocolumn are strings representing the address of each row.

伪列也类似于不带参数的 SQL 函数。不带参数的函数对于结果集中的每一行通常返回相同的值，而伪列通常为每个行返回不同的值。

• These strings have the data type ROWID. This pseudocolumn is not evident when listing the structure of a table by executing SELECT or DESCRIBE, nor does the pseudocolumn consume space.

ROWID 伪列的值是表示的每个行的地址的字符串。这些字符串具有的数据类型 ROWID。在执行 SELECT 或 DESCRIBE 列出表的结构时，此伪列并不显示，它也不占用空间。

• However, the rowid of each row can be retrieved with a SQL query using the reserved word ROWID as a column name.

但是，每个行的 rowid 可以通过使用保留字ROWID 作为列名的 SQL 查询来检索。

SQL> SELECT ROWID FROM employees WHERE employee_id = 100;

ROWID

------------------

AAAPecAAFAAAABSAAA

Format Models and Data Types

格式模型和数据类型

Format Models and Data Types

• A format model is a character literal that describes the format of datetime or numeric data stored in a character string.

格式模型是一个字符文本，用来描述存储在一个字符串中的日期时间或数值数据的格式。

• A format model does not change the internal representation of the value in the database.

格式模式不会更改数据库中的值的内部表示形式。

• When you convert a character string into a date or number, a format model determines how the database interprets the string.

当您将一个字符串转换成日期或数字时，格式模型决定了数据库如何解释字符串。

• In SQL, you can use a format model as an argument of the TO_CHAR and TO_DATE functions to format a value to be returned from the database or to format a value to be stored in the database.

在 SQL 中，你可以使用格式模型作为 TO_CHAR 和 TO_DATE 函数的参数，来格式化将从数据库中返回的一个值，或将存储到数据库中的一个值。

下面的语句选择部门 80 中的雇员的薪水，并使用 TO_CHAR 函数来将这些薪水的值，转换为以数字格式模型 ‘$ 99,990.99‘ 指定的字符值：

SQL> SELECT last_name employee, TO_CHAR(salary, ‘$99,990.99‘)

2 FROM employees

3 WHERE department_id = 80 AND last_name = ‘Russell‘;

EMPLOYEE TO_CHAR(SAL

------------------------- -----------

Russell $14,000.00

下面的示例更新一个雇佣日期，使用 TO_DATE 函数与格式掩码 ‘YYYYMM DD‘ 将字符串 ‘1998 05 20‘ 转换为日期值。

SQL> UPDATE employees

2 SET hire_date = TO_DATE(‘1998 05 20‘,‘YYYY MM DD‘)

3 WHERE last_name = ‘Hunold‘;

其他内建类型

Other important categories of built-in types include raw, large objects (LOBs), and collections. PL/SQL has data types for constants and variables, which include BOOLEAN, reference types, composite types (records), and user-defined types.

RAW、大对象 (LOB)、 和集合。 PL/SQL 具有用于常量和变量的数据类型，包括布尔、 引用类型、 复合类型 （记录） 、和用户定义类型