Oracle 视图 ALL_TAB_COLUMNS 官方解释,作用,如何使用详细说明

本站中文解释

Oracle视图all_tab_columns是一个系统视图,用于存储拥有者所具有访问权限的对象的表和列的编目信息,也就是系统中所有表和列的信息。

此视图可以用来检索特定表或者特定列的一些元数据信息,例如列名、类型、大小等等,我们也可以通过这个视图获取到某一数据库中的表的细节信息。

要使用all_tab_columns视图,请使用SELECT语句,可以指定要检索哪些列,以及查询条件(其中必须包含表名和列名),例如:

SELECT column_name, data_type, data_length
FROM all_tab_columns
WHERE table_name = ‘MyTable’ AND column_name IN (‘C1’, ‘C2’);

此查询在视图中搜索名为MyTable的表中的C1和C2两个列,并获取它们的名称、数据类型和数据长度的信息。

官方英文解释

ALL_TAB_COLUMNS describes the columns of the tables, views, and clusters accessible to the current user.

To gather statistics for this view, use the DBMS_STATS package.

This view filters out system-generated hidden columns. The ALL_TAB_COLS view does not filter out system-generated hidden columns.

Related Views

  • DBA_TAB_COLUMNS describes the columns of all tables, views, and clusters in the database.

  • USER_TAB_COLUMNS describes the columns of the tables, views, and clusters owned by the current user. This view does not display the OWNER column.

Column Datatype NULL Description

OWNER

VARCHAR2(128)

NOT NULL

Owner of the table, view, or cluster

TABLE_NAME

VARCHAR2(128)

NOT NULL

Name of the table, view, or cluster

COLUMN_NAME

VARCHAR2(128)

NOT NULL

Column name

DATA_TYPE

VARCHAR2(128)

Data type of the column

DATA_TYPE_MOD

VARCHAR2(3)

Data type modifier of the column

DATA_TYPE_OWNER

VARCHAR2(128)

Owner of the data type of the column

DATA_LENGTH

NUMBER

NOT NULL

Length of the column (in bytes)

DATA_PRECISION

NUMBER

Decimal precision for NUMBER data type; binary precision for FLOAT data type; NULL for all other data types

DATA_SCALE

NUMBER

Digits to the right of the decimal point in a number

NULLABLE

VARCHAR2(1)

Indicates whether a column allows NULLs. The value is N if there is a NOT NULL constraint on the column or if the column is part of a PRIMARY KEY. The constraint should be in an ENABLE VALIDATE state.

COLUMN_ID

NUMBER

Sequence number of the column as created

DEFAULT_LENGTH

NUMBER

Length of the default value for the column

DATA_DEFAULT

LONG

Default value for the column

NUM_DISTINCT

NUMBER

Number of distinct values in the column.

This column remains for backward compatibility with Oracle7. This information is now in the {TAB|PART}_COL_STATISTICS views.

LOW_VALUE

RAW(1000)

Low value in the column.

This column remains for backward compatibility with Oracle7. This information is now in the {TAB|PART}_COL_STATISTICS views.

HIGH_VALUE

RAW(1000)

High value in the column.

This column remains for backward compatibility with Oracle7. This information is now in the {TAB|PART}_COL_STATISTICS views.

DENSITY

NUMBER

If a histogram is available on COLUMN_NAME, then this column displays the selectivity of a value that spans fewer than 2 endpoints in the histogram. It does not represent the selectivity of values that span 2 or more endpoints.

If a histogram is not available on COLUMN_NAME, then the value of this column is 1/NUM_DISTINCT.

This column remains for backward compatibility with Oracle7. This information is now in the {TAB|PART}_COL_STATISTICS views.

NUM_NULLS

NUMBER

Number of NULLs in the column

NUM_BUCKETS

NUMBER

Number of buckets in the histogram for the column

Note: The number of buckets in a histogram is specified in the SIZE parameter of the ANALYZE SQL statement. However, Oracle Database does not create a histogram with more buckets than the number of rows in the sample. Also, if the sample contains any values that are very repetitious, Oracle Database creates the specified number of buckets, but the value indicated by this column may be smaller because of an internal compression algorithm.

LAST_ANALYZED

DATE

Date on which this column was most recently analyzed

SAMPLE_SIZE

NUMBER

Sample size used in analyzing this column

CHARACTER_SET_NAME

VARCHAR2(44)

Name of the character set:

  • CHAR_CS

  • NCHAR_CS

CHAR_COL_DECL_LENGTH

NUMBER

Declaration length of the character type column

GLOBAL_STATS

VARCHAR2(3)

GLOBAL_STATS will be YES if statistics are gathered or incrementally maintained, otherwise it will be NO

USER_STATS

VARCHAR2(3)

Indicates whether statistics were entered directly by the user (YES) or not (NO)

AVG_COL_LEN

NUMBER

Average length of the column (in bytes)

CHAR_LENGTH

NUMBER

Displays the length of the column in characters. This value only applies to the following datatypes:

  • CHAR

  • VARCHAR2

  • NCHAR

  • NVARCHAR2

CHAR_USED

VARCHAR2(1)

Indicates that the column uses BYTE length semantics (B) or CHAR length semantics (C), or whether the datatype is not any of the following (NULL):

  • CHAR

  • VARCHAR2

  • NCHAR

  • NVARCHAR2

V80_FMT_IMAGE

VARCHAR2(3)

Indicates whether the column data is in release 8.0 image format (YES) or not (NO)

DATA_UPGRADED

VARCHAR2(3)

Indicates whether the column data has been upgraded to the latest type version format (YES) or not (NO)

HISTOGRAM

VARCHAR2(15)

Indicates existence/type of histogram:

  • NONE

  • FREQUENCY

  • TOP-FREQUENCY

  • HEIGHT BALANCED

  • HYBRID

DEFAULT_ON_NULL

VARCHAR2(3)

Indicates whether the column has DEFAULT ON NULL semantics (YES) or not (NO)

IDENTITY_COLUMN

VARCHAR2(3)

Indicates whether this is an identity column (YES) or not (NO)

EVALUATION_EDITION

VARCHAR2(128)

Name of the edition in which editioned objects referenced in an expression column are resolved

UNUSABLE_BEFORE

VARCHAR2(128)

Name of the oldest edition in which the column is usable

UNUSABLE_BEGINNING

VARCHAR2(128)

Name of the oldest edition in which the column becomes perpetually unusable

COLLATION

VARCHAR2(100)

Collation for the column. Only applies to columns with character data types.

See Also:

  • “DBA_TAB_COLUMNS”

  • “USER_TAB_COLUMNS”

  • “ALL_TAB_COLS”

  • Oracle Database PL/SQL
    Packages and Types Reference
    for more information about the DBMS_STATS package


数据运维技术 » Oracle 视图 ALL_TAB_COLUMNS 官方解释,作用,如何使用详细说明