The first column of the returned result set is the subtable name, and the subsequent columns are the tag columns.
If you already know the name of the tag column, you can use the following statement to get the value of the specified tag column.
```
taos> SELECT DISTINCT TBNAME, id FROM st1;
tbname | id |
===============================================
st1s1 | 1 |
st1s2 | 2 |
st1s3 | 3 |
Query OK, 3 rows in database (0.002891s)
```
It should be noted that DISTINCT and TBNAME in the SELECT statement are essential, and TDengine will optimize the statement according to them, so that it can return the tag value correctly and quickly even when there is no data or a lot of data.
| 1 | vnodes | SMALLINT | Current number of vnodes on the dnode |
| 2 | vnodes | SMALLINT | Maximum number of vnodes on the dnode |
| 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 | BINARY(10) | Current status |
| 4 | note | BINARY(256) | Reason for going offline or other information |
| 5 | id | SMALLINT | Dnode ID |
...
...
@@ -49,16 +49,6 @@ Provides information about mnodes. Similar to SHOW MNODES.
| 4 | role_time | TIMESTAMP | Time at which the current role was assumed |
| 5 | create_time | TIMESTAMP | Creation time |
## INS_MODULES
Provides information about modules. Similar to SHOW MODULES.
Provides information about qnodes. Similar to SHOW QNODES.
...
...
@@ -88,33 +78,33 @@ Provides information about user-created databases. Similar to SHOW DATABASES.
| 1| name| BINARY(32)| 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 |
| 6 | replica | INT | Number of replicas |
| 7 | quorum | BINARY(3) | Strong consistency |
| 8 | duration | INT | Duration for storage of single files |
| 9 | keep | INT | Data retention period |
| 10 | buffer | INT | Write cache size per vnode, in MB |
| 11 | pagesize | INT | Page size for vnode metadata storage engine, in KB |
| 12 | pages | INT | Number of pages per vnode metadata storage engine |
| 13 | minrows | INT | Maximum number of records per file block |
| 14 | maxrows | INT | Minimum number of records per file block |
| 15 | comp | INT | Compression method |
| 16 | precision | BINARY(2) | Time precision |
| 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 | BINARY(3) | Strong consistency. It should be noted that `strict` is a TDengine keyword and needs to be escaped with ` when used as a column name. |
| 8 | duration | INT | 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 | INT | 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 | BINARY(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 | BINARY(10) | Current database status |
| 18 | retention | BINARY (60) | Aggregation interval and retention period |
| 19 | single_stable | BOOL | Whether the database can contain multiple supertables |
| 20 | cachemodel | BINARY(60) | Caching method for the newest data |
| 21 | cachesize | INT | Memory per vnode used for caching the newest data |
| 22 | wal_level | INT | WAL level |
| 23 | wal_fsync_period | INT | Interval at which WAL is written to disk |
| 24 | wal_retention_period | INT | WAL retention period |
| 25 | wal_retention_size | INT | Maximum WAL size |
| 26 | wal_roll_period | INT | WAL rotation period |
| 28 | stt_trigger | SMALLINT | The threshold for number of files to trigger file merging |
| 29 | table_prefix | SMALLINT | The prefix length in the table name that is ignored when distributing table to vnode based on table name |
| 30 | table_suffix | SMALLINT | The suffix length in the table name that is ignored when distributing table to vnode based on table name |
| 31 | tsdb_pagesize | INT | The page size for internal storage engine, its unit is KB |
| 18 | retentions | BINARY (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 | BINARY(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. 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 | wal_roll_period | INT | WAL rotation period. It should be noted that `wal_roll_period` is a TDengine keyword and needs to be escaped with ` when used as a column name. |
| 27 | wal_segment_size | BIGINT | WAL file size. It should be noted that `wal_segment_size` is a TDengine keyword and needs to be escaped with ` when used as a column name. |
| 28 | 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. |
| 29 | 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. |
| 30 | 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. |
| 31 | 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
...
...
@@ -123,8 +113,8 @@ Provides information about user-defined functions.
| 2 | comment | BINARY(255) | Function description |
| 3 | aggregate | INT | Whether the UDF is an aggregate function |
| 2 | comment | BINARY(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 | BINARY(31) | Output data type |
| 5 | create_time | TIMESTAMP | Creation time |
| 6 | code_len | INT | Length of the source code |
...
...
@@ -153,12 +143,12 @@ Provides information about supertables.
| 2 | db_name | BINARY(64) | All databases in the supertable |
| 3 | create_time | TIMESTAMP | Creation time |
| 4 | columns | INT | Number of columns |
| 5 | tags | INT | Number of tags |
| 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 |
| 8 | watermark | BINARY(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 | BINARY(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 | BINARY(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
...
...
@@ -173,7 +163,7 @@ Provides information about standard tables and subtables.
| 5 | stable_name | BINARY(192) | Supertable name |
| 6 | uid | BIGINT | Table ID |
| 7 | vgroup_id | INT | Vgroup ID |
| 8 | ttl | INT | Table time-to-live |
| 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. |
| 1 | version | BINARY(9) | Whether the deployment is a licensed or trial version |
| 2 | cpu_cores | BINARY(9) | CPU cores included in license |
| 3 | dnodes | BINARY(10) | Dnodes included in license |
| 4 | streams | BINARY(10) | Streams included in license |
| 5 | users | BINARY(10) | Users included in license |
| 6 | streams | BINARY(10) | Accounts included in license |
| 7 | storage | BINARY(21) | Storage space included in license |
| 8 | connections | BINARY(21) | Client connections included in license |
| 9 | databases | BINARY(11) | Databases included in license |
| 3 | dnodes | BINARY(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 | BINARY(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 | BINARY(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 | BINARY(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 | BINARY(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 | BINARY(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 | BINARY(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 | BINARY(9) | Write speed specified in license (data points per second) |
| 11 | querytime | BINARY(9) | Total query time specified in license |
| 12 | timeseries | BINARY(21) | Number of metrics included in license |
...
...
@@ -227,7 +217,7 @@ Provides information about vgroups.
| 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 | BINARY(10) | Vgroup status |
| 5 | v1_dnode | INT | Dnode ID of first vgroup member |
| 6 | v1_status | BINARY(10) | Status of first vgroup member |
...
...
@@ -246,7 +236,7 @@ Provides system configuration information.
| 9 | trigger | INT | Method of triggering the result push (see stream processing documentation) |
| 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. |
