学步园

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VARCHAR2(size [BYTE | CHAR])

Variable-length(可变的长) character string having maximum length size bytes
or characters. Maximum sizeis 4000 bytes or characters, and minimum is 1 byte or 1 character. You must specify(指定) size for VARCHAR2.

BYTE indicates that the column will have byte length semantics. CHAR indicates that the column will have character semantics.

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NVARCHAR2(size)

Variable-length Unicode character string having maximum length size characters. The number of bytes can
be up to two times size for AL16UTF16 encoding(编码) and
three times size for UTF8 encoding.
Maximum size isdetermined(决定) by
the national character set definition(定义), with an upper limit(限制) of 4000 bytes. You mustspecify size for NVARCHAR2.

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NUMBER [ (p [, s])
]

Number having precision(精确度) p and scale(小数) s.
The precision p can range from 1 to 38. The scale s can
range from -84 to 127. Both precision andscale are in decimal digits(十进制小数). A NUMBER valuerequires(规定) from
1 to 22 bytes.

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FLOAT [(p)]

A subtype of the NUMBER data type having precision p.
A FLOAT value is represented(代表) internally(内部) as NUMBER. The precision p can
range from 1 to 126binary digits(二进制). A FLOAT value requires from 1 to 22 bytes.

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LONG

Character data of variable length up to 2 gigabytes, or 2³¹ -1 bytes. Provided for backwardcompatibility(兼容).

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DATE

Valid(有效的) date range from January 1, 4712 BC, to December 31, 9999 AD. The default format isdetermined(决定) explicitly(明确) by
the NLS_DATE_FORMAT parameter(参数) or implicitly(绝对的) by the NLS_TERRITORYparameter. The size is fixed(固定) at
7 bytes. This data type contains(包含) the datetime fields(字段) YEAR, MONTH,DAY, HOUR, MINUTE, and SECOND.
It does not have fractional seconds(分数秒)or a time zone(时区).

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BINARY_FLOAT

32-bit floating point number. This data type requires 4 bytes.

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BINARY_DOUBLE

64-bit floating point number. This data type requires 8 bytes.

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TIMESTAMP [(fractional_seconds_precision)]

Year, month, and day values of date, as well as hour, minute, and second values of time, where fractional_seconds_precision is
the number ofdigits(数字) in the fractional part of the SECOND(次要) datetime field. Accepted(公认的) values
of fractional_seconds_precision are 0 to 9. The default is 6. The default format is determined explicitly by the NLS_TIMESTAMP_FORMAT parameter or implicitly(绝对的) by
theNLS_TERRITORY parameter. The size is 7 or 11 bytes, depending(依赖) on the precision(精度). This data type contains(包含) the
datetime fields YEAR, MONTH, DAY, HOUR, MINUTE, and SECOND. Itcontains fractional(包含) seconds but does
not have a time zone.

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TIMESTAMP [(fractional_seconds)] WITH TIME ZONE

All values of TIMESTAMP as well as time zonedisplacement(替代) value, where fractional_seconds_precision is
the number of digitsin the fractional part of the SECOND datetime field.Accepted values
are 0 to 9. The default is 6. The default format is determined explicitly by the NLS_TIMESTAMP_FORMAT parameter or implicitly by the NLS_TERRITORY parameter. The size is fixed(固定) at
13 bytes. This data type contains the datetime fields YEAR, MONTH, DAY, HOUR, MINUTE, SECOND,TIMEZONE_HOUR, and TIMEZONE_MINUTE.
It has fractional seconds and an explicit time zone.

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TIMESTAMP [(fractional_seconds)] WITH LOCAL TIME ZONE

All values of TIMESTAMP WITH TIME ZONE, with the following exceptions:

• Data is normalized(规范的) to the database time zone when it is stored in the database.

• When the data is retrieved(检查), users see the data in the session time zone.

The default format is determined explicitly by the NLS_TIMESTAMP_FORMAT parameter or implicitly by the NLS_TERRITORY parameter. The size is 7 or 11 bytes, depending on the precision(精度).

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INTERVAL YEAR [(year_precision)] TO MONTH

Stores(储存) a period(阶段) of time in years and months, where year_precision is the
number of digits(位数) in theYEAR datetime field. Accepted(公认的) values are 0 to 9. The default is 2. The size is fixed at 5 bytes.

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INTERVAL DAY [(day_precision)] TO SECOND[(fractional_seconds)]

Stores a period of time in days, hours, minutes, and seconds, where

• day_precision is the maximum number of digits in the DAY datetime field. Accepted values
  are 0 to 9. The default is 2.

• fractional_seconds_precision is the number of digits in the fractional part of the SECONDfield.
  Accepted values are 0 to 9. The default is 6.

The size is fixed at 11 bytes.

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RAW(size)

Raw(最初的) binary data of length size bytes. Maximum size is
2000 bytes. You must specify size for a RAW value.

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LONG RAW

Raw binary data of variable length up to 2 gigabytes.

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ROWID

Base 64 string representing(代表) the unique address of a row in its table(地址). This data type isprimarily(主要的) for
values returned by the ROWID pseudocolumn.

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UROWID [(size)]

Base 64 string representing the logical(逻辑) address of a row of an index-organized table. The optionalsize is the
size of(..大小) a column of type UROWID. The maximum size and default is 4000 bytes.

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CHAR [(size [BYTE | CHAR])]

Fixed(固定)-length character data of length size bytes or characters.
Maximum size is 2000 bytes or characters. Default and minimum size is
1 byte.

BYTE and CHAR have the same semantics(语法) asfor VARCHAR2.

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NCHAR[(size)]

Fixed-length character data of length size characters.The number of(..的数量) bytes
can be up to two times size for AL16UTF16 encoding and three times size for UTF8 encoding.
Maximum size isdetermined(决定) by the national character setdefinition(定义), with
an upper limit of 2000 bytes. Default and minimum size is 1 character.

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CLOB

A character large object containing single(单)-byte ormultibyte(多字节) characters. Both fixed-width andvariable(变化的)-width character
sets(字符集) aresupported(支持的), both using the database character set. Maximum size is (4 gigabytes - 1) * (database block size).

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NCLOB

A character large object containing Unicode characters. Both fixed-width and variable-width character sets are supported, both using the databasenational character
set. Maximum size is (4 gigabytes - 1) * (database block(块) size). Stores nationalcharacter set data.

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BLOB

A binary large object. Maximum size is (4 gigabytes - 1) * (database block size).

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BFILE

Contains a locator(位置) to a large(多数的) binary file stored (存信息的) outside the database.Enables(使..) byte stream(流) I/O
access toexternal(外部的) LOBs residing on the database server. Maximum size is 4 gigabytes.