homework-jianmu/docs/en/12-taos-sql/22-meta.md

title	sidebar_label	description
Information_Schema Database	Metadata	This document describes how to use the INFORMATION_SCHEMA database in TDengine.

TDengine includes a built-in database named INFORMATION_SCHEMA to provide access to database metadata, system information, and status information. This information includes database names, table names, and currently running SQL statements. All information related to TDengine maintenance is stored in this database. It contains several read-only tables. These tables are more accurately described as views, and they do not correspond to specific files. You can query these tables but cannot write data to them. The INFORMATION_SCHEMA database is intended to provide a unified method for SHOW commands to access data. However, using SELECT ... FROM INFORMATION_SCHEMA.tablename offers several advantages over SHOW commands:

1. You can use a USE statement to specify the INFORMATION_SCHEMA database as the current database.
2. You can use the familiar SELECT syntax to access information, provided that you know the table and column names.
3. You can filter and order the query results. More generally, you can use any SELECT syntax that TDengine supports to query the INFORMATION_SCHEMA database.
4. Future versions of TDengine can add new columns to INFORMATION_SCHEMA tables without affecting existing business systems.
5. It is easier for users coming from other database management systems. For example, Oracle users can query data dictionary tables.

:::info

• SHOW statements are still supported for the convenience of existing users.
• Some columns in the system table may be keywords, and you need to use the escape character '`' when querying, for example, to query the VGROUPS in the database test:

   select `vgroups` from ins_databases where name = 'test';

:::

This document introduces the tables of INFORMATION_SCHEMA and their structure.

INS_DNODES

Provides information about dnodes. Similar to SHOW DNODES. Users whose SYSINFO attribute is 0 can't view this table.

#	Column	Data Type	Description
1	vnodes	SMALLINT	Current number of vnodes on the dnode. It should be noted that vnodes is a TDengine keyword and needs to be escaped with ` when used as a column name.
2	support_vnodes	SMALLINT	Maximum number of vnodes on the dnode
3	status	VARCHAR(10)	Current status
4	note	VARCHAR(256)	Reason for going offline or other information
5	id	SMALLINT	Dnode ID
6	endpoint	VARCHAR(134)	Dnode endpoint
7	create	TIMESTAMP	Creation time

INS_MNODES

Provides information about mnodes. Similar to SHOW MNODES. Users whose SYSINFO attribute is 0 can't view this table.

#	Column	Data Type	Description
1	id	SMALLINT	Mnode ID
2	endpoint	VARCHAR(134)	Mnode endpoint
3	role	VARCHAR(10)	Current role
4	role_time	TIMESTAMP	Time at which the current role was assumed
5	create_time	TIMESTAMP	Creation time

INS_QNODES

Provides information about qnodes. Similar to SHOW QNODES. Users whose SYSINFO attribute is 0 can't view this table.

#	Column	Data Type	Description
1	id	SMALLINT	Qnode ID
2	endpoint	VARCHAR(134)	Qnode endpoint
3	create_time	TIMESTAMP	Creation time

INS_SNODES

Provides information about snodes. Similar to SHOW SNODES. Users whose SYSINFO attribute is 0 can't view this table.

#	Column	Data Type	Description
1	id	SMALLINT	Snode ID
2	endpoint	VARCHAR(134)	Snode endpoint
3	create_time	TIMESTAMP	Creation time

INS_CLUSTER

Provides information about the cluster. Users whose SYSINFO attribute is 0 can't view this table.

#	Column	Data Type	Description
1	id	BIGINT	Cluster ID
2	name	VARCHAR(134)	Cluster name
3	create_time	TIMESTAMP	Creation time

INS_DATABASES

Provides information about user-created databases. Similar to SHOW DATABASES.

#	Column	Data Type	Description
1	name	VARCHAR(64)	Database name
2	create_time	TIMESTAMP	Creation time
3	ntables	INT	Number of standard tables and subtables (not including supertables)
4	vgroups	INT	Number of vgroups. It should be noted that vnodes is a TDengine keyword and needs to be escaped with ` when used as a column name.
6	replica	INT	Number of replicas. It should be noted that replica is a TDengine keyword and needs to be escaped with ` when used as a column name.
7	strict	VARCHAR(4)	Obsoleted
8	duration	VARCHAR(10)	Duration for storage of single files. It should be noted that duration is a TDengine keyword and needs to be escaped with ` when used as a column name.
9	keep	VARCHAR(32)	Data retention period. It should be noted that keep is a TDengine keyword and needs to be escaped with ` when used as a column name.
10	buffer	INT	Write cache size per vnode, in MB. It should be noted that buffer is a TDengine keyword and needs to be escaped with ` when used as a column name.
11	pagesize	INT	Page size for vnode metadata storage engine, in KB. It should be noted that pagesize is a TDengine keyword and needs to be escaped with ` when used as a column name.
12	pages	INT	Number of pages per vnode metadata storage engine. It should be noted that pages is a TDengine keyword and needs to be escaped with ` when used as a column name.
13	minrows	INT	Maximum number of records per file block. It should be noted that minrows is a TDengine keyword and needs to be escaped with ` when used as a column name.
14	maxrows	INT	Minimum number of records per file block. It should be noted that maxrows is a TDengine keyword and needs to be escaped with ` when used as a column name.
15	comp	INT	Compression method. It should be noted that comp is a TDengine keyword and needs to be escaped with ` when used as a column name.
16	precision	VARCHAR(2)	Time precision. It should be noted that precision is a TDengine keyword and needs to be escaped with ` when used as a column name.
17	status	VARCHAR(10)	Current database status
18	retentions	VARCHAR(60)	Aggregation interval and retention period. It should be noted that retentions is a TDengine keyword and needs to be escaped with ` when used as a column name.
19	single_stable	BOOL	Whether the database can contain multiple supertables. It should be noted that single_stable is a TDengine keyword and needs to be escaped with ` when used as a column name.
20	cachemodel	VARCHAR(60)	Caching method for the newest data. It should be noted that cachemodel is a TDengine keyword and needs to be escaped with ` when used as a column name.
21	cachesize	INT	Memory per vnode used for caching the newest data. It should be noted that cachesize is a TDengine keyword and needs to be escaped with ` when used as a column name.
22	wal_level	INT	WAL level. It should be noted that wal_level is a TDengine keyword and needs to be escaped with ` when used as a column name.
23	wal_fsync_period	INT	Interval at which WAL is written to disk. It should be noted that wal_fsync_period is a TDengine keyword and needs to be escaped with ` when used as a column name.
24	wal_retention_period	INT	WAL retention period, in second. It should be noted that wal_retention_period is a TDengine keyword and needs to be escaped with ` when used as a column name.
25	wal_retention_size	INT	Maximum WAL size. It should be noted that wal_retention_size is a TDengine keyword and needs to be escaped with ` when used as a column name.
26	stt_trigger	SMALLINT	The threshold for number of files to trigger file merging. It should be noted that stt_trigger is a TDengine keyword and needs to be escaped with ` when used as a column name.
27	table_prefix	SMALLINT	The prefix length in the table name that is ignored when distributing table to vnode based on table name. It should be noted that table_prefix is a TDengine keyword and needs to be escaped with ` when used as a column name.
28	table_suffix	SMALLINT	The suffix length in the table name that is ignored when distributing table to vnode based on table name. It should be noted that table_suffix is a TDengine keyword and needs to be escaped with ` when used as a column name.
29	tsdb_pagesize	INT	The page size for internal storage engine, its unit is KB. It should be noted that tsdb_pagesize is a TDengine keyword and needs to be escaped with ` when used as a column name.

INS_FUNCTIONS

Provides information about user-defined functions.

#	Column	Data Type	Description
1	name	VARCHAR(64)	Function name
2	comment	VARCHAR(255)	Function description. It should be noted that comment is a TDengine keyword and needs to be escaped with ` when used as a column name.
3	aggregate	INT	Whether the UDF is an aggregate function. It should be noted that aggregate is a TDengine keyword and needs to be escaped with ` when used as a column name.
4	output_type	VARCHAR(31)	Output data type
5	create_time	TIMESTAMP	Creation time
6	code_len	INT	Length of the source code
7	bufsize	INT	Buffer size
8	func_language	VARCHAR(31)	UDF programming language
9	func_body	VARCHAR(16384)	UDF function body
10	func_version	INT	UDF function version. starting from 0. Increasing by 1 each time it is updated

INS_INDEXES

Provides information about user-created indices. Similar to SHOW INDEX.

#	Column	Data Type	Description
1	db_name	VARCHAR(32)	Database containing the table with the specified index
2	table_name	VARCHAR(192)	Table containing the specified index
3	index_name	VARCHAR(192)	Index name
4	db_name	VARCHAR(64)	Index column
5	index_type	VARCHAR(10)	SMA or tag index
6	index_extensions	VARCHAR(256)	Other information For SMA/tag indices, this shows a list of functions

INS_STABLES

Provides information about supertables.

#	Column	Data Type	Description
1	stable_name	VARCHAR(192)	Supertable name
2	db_name	VARCHAR(64)	All databases in the supertable
3	create_time	TIMESTAMP	Creation time
4	columns	INT	Number of columns
5	tags	INT	Number of tags. It should be noted that tags is a TDengine keyword and needs to be escaped with ` when used as a column name.
6	last_update	TIMESTAMP	Last updated time
7	table_comment	VARCHAR(1024)	Table description
8	watermark	VARCHAR(64)	Window closing time. It should be noted that watermark is a TDengine keyword and needs to be escaped with ` when used as a column name.
9	max_delay	VARCHAR(64)	Maximum delay for pushing stream processing results. It should be noted that max_delay is a TDengine keyword and needs to be escaped with ` when used as a column name.
10	rollup	VARCHAR(128)	Rollup aggregate function. It should be noted that rollup is a TDengine keyword and needs to be escaped with ` when used as a column name.

INS_TABLES

Provides information about standard tables and subtables.

#	Column	Data Type	Description
1	table_name	VARCHAR(192)	Table name
2	db_name	VARCHAR(64)	Database name
3	create_time	TIMESTAMP	Creation time
4	columns	INT	Number of columns
5	stable_name	VARCHAR(192)	Supertable name
6	uid	BIGINT	Table ID
7	vgroup_id	INT	Vgroup ID
8	ttl	INT	Table time-to-live. It should be noted that ttl is a TDengine keyword and needs to be escaped with ` when used as a column name.
9	table_comment	VARCHAR(1024)	Table description
10	type	VARCHAR(20)	Table type

INS_TAGS

#	Column	Data Type	Description
1	table_name	VARCHAR(192)	Table name
2	db_name	VARCHAR(64)	Database name
3	stable_name	VARCHAR(192)	Supertable name
4	tag_name	VARCHAR(64)	Tag name
5	tag_type	VARCHAR(64)	Tag type
6	tag_value	VARCHAR(16384)	Tag value

INS_COLUMNS

#	Column	Data Type	Description
1	table_name	VARCHAR(192)	Table name
2	db_name	VARCHAR(64)	Database name
3	table_type	VARCHAR(21)	Table type
4	col_name	VARCHAR(64)	Column name
5	col_type	VARCHAR(32)	Column type
6	col_length	INT	Column length
7	col_precision	INT	Column precision
8	col_scale	INT	Column scale
9	col_nullable	INT	Column nullable

INS_USERS

Provides information about TDengine users. Users whose SYSINFO attribute is 0 can't view this table.

#	Column	Data Type	Description
1	user_name	VARCHAR(23)	User name
2	privilege	VARCHAR(256)	User permissions
3	create_time	TIMESTAMP	Creation time

INS_GRANTS

Provides information about TDengine Enterprise Edition permissions. Users whose SYSINFO attribute is 0 can't view this table.

#	Column	Data Type	Description
1	version	VARCHAR(9)	Whether the deployment is a licensed or trial version
2	cpu_cores	VARCHAR(9)	CPU cores included in license
3	dnodes	VARCHAR(10)	Dnodes included in license. It should be noted that dnodes is a TDengine keyword and needs to be escaped with ` when used as a column name.
4	streams	VARCHAR(10)	Streams included in license. It should be noted that streams is a TDengine keyword and needs to be escaped with ` when used as a column name.
5	users	VARCHAR(10)	Users included in license. It should be noted that users is a TDengine keyword and needs to be escaped with ` when used as a column name.
6	accounts	VARCHAR(10)	Accounts included in license. It should be noted that accounts is a TDengine keyword and needs to be escaped with ` when used as a column name.
7	storage	VARCHAR(21)	Storage space included in license. It should be noted that storage is a TDengine keyword and needs to be escaped with ` when used as a column name.
8	connections	VARCHAR(21)	Client connections included in license. It should be noted that connections is a TDengine keyword and needs to be escaped with ` when used as a column name.
9	databases	VARCHAR(11)	Databases included in license. It should be noted that databases is a TDengine keyword and needs to be escaped with ` when used as a column name.
10	speed	VARCHAR(9)	Write speed specified in license (data points per second)
11	querytime	VARCHAR(9)	Total query time specified in license
12	timeseries	VARCHAR(21)	Number of metrics included in license
13	expired	VARCHAR(5)	Whether the license has expired
14	expire_time	VARCHAR(19)	When the trial period expires

INS_VGROUPS

Provides information about vgroups. Users whose SYSINFO attribute is 0 can't view this table.

#	Column	Data Type	Description
1	vgroup_id	INT	Vgroup ID
2	db_name	VARCHAR(32)	Database name
3	tables	INT	Tables in vgroup. It should be noted that tables is a TDengine keyword and needs to be escaped with ` when used as a column name.
4	status	VARCHAR(10)	Vgroup status
5	v1_dnode	INT	Dnode ID of first vgroup member
6	v1_status	VARCHAR(10)	Status of first vgroup member
7	v2_dnode	INT	Dnode ID of second vgroup member
8	v2_status	VARCHAR(10)	Status of second vgroup member
9	v3_dnode	INT	Dnode ID of third vgroup member
10	v3_status	VARCHAR(10)	Status of third vgroup member
11	nfiles	INT	Number of data and metadata files in the vgroup
12	file_size	INT	Size of the data and metadata files in the vgroup
13	tsma	TINYINT	Whether time-range-wise SMA is enabled. 1 means enabled; 0 means disabled.

INS_CONFIGS

Provides system configuration information.

#	Column	Data Type	Description
1	name	VARCHAR(32)	Parameter
2	value	VARCHAR(64)	Value. It should be noted that value is a TDengine keyword and needs to be escaped with ` when used as a column name.

INS_DNODE_VARIABLES

Provides dnode configuration information. Users whose SYSINFO attribute is 0 can't view this table.

#	Column	Data Type	Description
1	dnode_id	INT	Dnode ID
2	name	VARCHAR(32)	Parameter
3	value	VARCHAR(64)	Value. It should be noted that value is a TDengine keyword and needs to be escaped with ` when used as a column name.

INS_TOPICS

#	Column	Data Type	Description
1	topic_name	VARCHAR(192)	Topic name
2	db_name	VARCHAR(64)	Database for the topic
3	create_time	TIMESTAMP	Creation time
4	sql	VARCHAR(1024)	SQL statement used to create the topic

INS_SUBSCRIPTIONS

#	Column	Data Type	Description
1	topic_name	VARCHAR(204)	Subscribed topic
2	consumer_group	VARCHAR(193)	Subscribed consumer group
3	vgroup_id	INT	Vgroup ID for the consumer
4	consumer_id	BIGINT	Consumer ID
5	offset	VARCHAR(64)	Consumption progress
6	rows	BIGINT	Number of consumption items

INS_STREAMS

#	Column	Data Type	Description
1	stream_name	VARCHAR(64)	Stream name
2	create_time	TIMESTAMP	Creation time
3	sql	VARCHAR(1024)	SQL statement used to create the stream
4	status	VARCHAR(20)	Current status
5	source_db	VARCHAR(64)	Source database
6	target_db	VARCHAR(64)	Target database
7	target_table	VARCHAR(192)	Target table
8	watermark	BIGINT	Watermark (see stream processing documentation). It should be noted that watermark is a TDengine keyword and needs to be escaped with ` when used as a column name.
9	trigger	INT	Method of triggering the result push (see stream processing documentation). It should be noted that trigger is a TDengine keyword and needs to be escaped with ` when used as a column name.

INS_USER_PRIVILEGES

Users whose SYSINFO attribute is 0 can't view this table.

| # | Column | Data Type | Description |** | | --- | :----------: | ------------ | -------------------------------------------| | 1 | user_name | VARCHAR(24) | Username | | 2 | privilege | VARCHAR(10) | Privilege description | | 3 | db_name | VARCHAR(65) | Database name | | 4 | table_name | VARCHAR(193) | Table name | | 5 | condition | VARCHAR(49152) | The privilege filter for child tables |