Oracle 视图 ALL_TAB_COLS 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_COLS是一个多表视图，其中用于存储用户在Oracle数据库中拥有的表、表列和索引的元数据信息。

此视图可以帮助用户快速了解Oracle数据库中正在使用的表列名称、表空间、占用空间大小等信息，从而成功实施数据库管理项目。

使用视图ALL_TAB_COLS的方法如下：

1、查询一个表的全部列：
SELECT * FROM ALL_TAB_COLS WHERE TABLE_NAME=’TABLE_NAME’;

2、查询一个表的指定列信息：
SELECT * FROM ALL_TAB_COLS WHERE TABLE_NAME=’TABLE_NAME’ AND COLUMN_NAME=’COLUMN_NAME’;

3、按照表中列名排序：
SELECT * FROM ALL_TAB_COLS WHERE TABLE_NAME=’TABLE_NAME’ ORDER BY COLUMN_NAME;

4、查询用户拥有的每个表的索引列：
SELECT TABLE_NAME,UNIQUENESS,COLUMN_NAME,INDEX_NAME,COLUMN_LENGTH
FROM ALL_TAB_COLS WHERE TABLE_NAME IN (SELECT TABLE_NAME
FROM ALL_TABLES WHERE OWNER=’your_owner’) AND INDEX_NAME IS NOT NULL;

官方英文解释

ALL_TAB_COLS 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 differs from ALL_TAB_COLUMNS in that system-generated hidden columns are not filtered out.

Related Views

DBA_TAB_COLS describes the columns of all tables, views, and clusters in the database.
USER_TAB_COLS 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` datatype; binary precision for `FLOAT` datatype; NULL for all other datatypes
`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`.
`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`)
`HIDDEN_COLUMN`	`VARCHAR2(3)`		Indicates whether the column is a hidden column (`YES`) or not (`NO`)
`VIRTUAL_COLUMN`	`VARCHAR2(3)`		Indicates whether the column is a virtual column (`YES`) or not (`NO`)
`SEGMENT_COLUMN_ID`	`NUMBER`		Sequence number of the column in the segment
`INTERNAL_COLUMN_ID`	`NUMBER`	`NOT NULL`	Internal sequence number of the column
`HISTOGRAM`	`VARCHAR2(15)`		Indicates existence/type of histogram: `NONE` `FREQUENCY` `TOP-FREQUENCY` `HEIGHT BALANCED` `HYBRID`
`QUALIFIED_COL_NAME`	`VARCHAR2(4000)`		Qualified column name
`USER_GENERATED`	`VARCHAR2(3)`		Indicates whether the column is a user-generated column (`YES`) or a system-generated column (`NO`). Invisible columns are hidden columns that are also user- generated columns.
`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.
`COLLATED_COLUMN_ID`	`NUMBER`		Internal sequence number of a column, for which this virtual column generates a collation key.