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DESCRIBE
DO
DROP [GLOBAL|SESSION] BINDING
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COLUMNS
COLUMNS
表提供了表的所有列的信息。
USE information_schema;
DESC columns;
+--------------------------+---------------+------+------+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------------------------+---------------+------+------+---------+-------+
| TABLE_CATALOG | varchar(512) | YES | | NULL | |
| TABLE_SCHEMA | varchar(64) | YES | | NULL | |
| TABLE_NAME | varchar(64) | YES | | NULL | |
| COLUMN_NAME | varchar(64) | YES | | NULL | |
| ORDINAL_POSITION | bigint(64) | YES | | NULL | |
| COLUMN_DEFAULT | text | YES | | NULL | |
| IS_NULLABLE | varchar(3) | YES | | NULL | |
| DATA_TYPE | varchar(64) | YES | | NULL | |
| CHARACTER_MAXIMUM_LENGTH | bigint(21) | YES | | NULL | |
| CHARACTER_OCTET_LENGTH | bigint(21) | YES | | NULL | |
| NUMERIC_PRECISION | bigint(21) | YES | | NULL | |
| NUMERIC_SCALE | bigint(21) | YES | | NULL | |
| DATETIME_PRECISION | bigint(21) | YES | | NULL | |
| CHARACTER_SET_NAME | varchar(32) | YES | | NULL | |
| COLLATION_NAME | varchar(32) | YES | | NULL | |
| COLUMN_TYPE | text | YES | | NULL | |
| COLUMN_KEY | varchar(3) | YES | | NULL | |
| EXTRA | varchar(30) | YES | | NULL | |
| PRIVILEGES | varchar(80) | YES | | NULL | |
| COLUMN_COMMENT | varchar(1024) | YES | | NULL | |
| GENERATION_EXPRESSION | text | NO | | NULL | |
+--------------------------+---------------+------+------+---------+-------+
21 rows in set (0.00 sec)
CREATE TABLE test.t1 (a int);
SELECT * FROM columns WHERE table_schema='test' AND TABLE_NAME='t1'\G
*************************** 1. row ***************************
TABLE_CATALOG: def
TABLE_SCHEMA: test
TABLE_NAME: t1
COLUMN_NAME: a
ORDINAL_POSITION: 1
COLUMN_DEFAULT: NULL
IS_NULLABLE: YES
DATA_TYPE: int
CHARACTER_MAXIMUM_LENGTH: NULL
CHARACTER_OCTET_LENGTH: NULL
NUMERIC_PRECISION: 11
NUMERIC_SCALE: 0
DATETIME_PRECISION: NULL
CHARACTER_SET_NAME: NULL
COLLATION_NAME: NULL
COLUMN_TYPE: int(11)
COLUMN_KEY:
EXTRA:
PRIVILEGES: select,insert,update,references
COLUMN_COMMENT:
GENERATION_EXPRESSION:
1 row in set (0.02 sec)
COLUMNS
表中列的含义如下:
TABLE_CATALOG
:包含列的表所属的目录的名称。该值始终为def
。TABLE_SCHEMA
:包含列的表所属的数据库的名称。TABLE_NAME
:包含列的表的名称。COLUMN_NAME
:列的名称。ORDINAL_POSITION
:表中列的位置。COLUMN_DEFAULT
:列的默认值。如果列的显式默认值为NULL
,或者列定义中不包含default
子句,则此值为NULL
。IS_NULLABLE
:列的可空性。如果列中可以存储空值,则该值为YES
,否则为NO
。DATA_TYPE
:列的数据类型。CHARACTER_MAXIMUM_LENGTH
:对于字符串列,以字符为单位的最大长度。CHARACTER_OCTET_LENGTH
:对于字符串列,以字节为单位的最大长度。NUMERIC_PRECISION
:对于数字列,为数字精度。NUMERIC_SCALE
:对于数字列,为数字刻度。DATETIME_PRECISION
:对于时间列,小数秒精度。CHARACTER_SET_NAME
:对于字符串列,字符集名称。COLLATION_NAME
:对于字符串列,排序规则名称。COLUMN_TYPE
:列类型。COLUMN_KEY
:该列是否被索引。具体显示如下:- 如果此值为空,则该列要么未被索引,要么被索引且是多列非唯一索引中的第二列。
- 如果此值是
PRI
,则该列是主键,或者是多列主键中的一列。 - 如果此值是
UNI
,则该列是唯一索引的第一列。 - 如果此值是
MUL
,则该列是非唯一索引的第一列,在该列中允许给定值的多次出现。
EXTRA
:关于给定列的任何附加信息。PRIVILEGES
:当前用户对该列拥有的权限。目前在 TiDB 中,此值为定值,一直为select,insert,update,references
。COLUMN_COMMENT
:列定义中包含的注释。GENERATION_EXPRESSION
:对于生成的列,显示用于计算列值的表达式。对于未生成的列为空。
对应的 SHOW
语句如下:
SHOW COLUMNS FROM t1 FROM test;
+-------+---------+------+------+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+------+---------+-------+
| a | int(11) | YES | | NULL | |
+-------+---------+------+------+---------+-------+
1 row in set (0.00 sec)
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