docs: improve the system table chapter
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@ -11,7 +11,15 @@ TDengine includes a built-in database named `INFORMATION_SCHEMA` to provide acce
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4. Future versions of TDengine can add new columns to INFORMATION_SCHEMA tables without affecting existing business systems.
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4. Future versions of TDengine can add new columns to INFORMATION_SCHEMA tables without affecting existing business systems.
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5. It is easier for users coming from other database management systems. For example, Oracle users can query data dictionary tables.
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5. It is easier for users coming from other database management systems. For example, Oracle users can query data dictionary tables.
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Note: SHOW statements are still supported for the convenience of existing users.
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:::info
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- SHOW statements are still supported for the convenience of existing users.
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- Some columns in the system table may be keywords, and you need to use the escape character '\`' when querying, for example, the query database test has several VGROUPs:
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```sql
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select `vgroups` from ins_databases where name = 'test';
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```
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:::
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This document introduces the tables of INFORMATION_SCHEMA and their structure.
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This document introduces the tables of INFORMATION_SCHEMA and their structure.
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@ -102,7 +110,11 @@ Provides information about user-created databases. Similar to SHOW DATABASES.
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| 24 | wal_retention_period | INT | WAL retention period |
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| 24 | wal_retention_period | INT | WAL retention period |
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| 25 | wal_retention_size | INT | Maximum WAL size |
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| 25 | wal_retention_size | INT | Maximum WAL size |
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| 26 | wal_roll_period | INT | WAL rotation period |
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| 26 | wal_roll_period | INT | WAL rotation period |
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| 27 | wal_segment_size | WAL file size |
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| 27 | wal_segment_size | BIGINT | WAL file size |
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| 28 | stt_trigger | SMALLINT | The number of files placed on the disk that trigger file merging |
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| 29 | table_prefix | SMALLINT | The table name is used for the prefix length that needs to be ignored when calculating the consistent HASH |
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| 30 | table_suffix | SMALLINT | The table name is used for the suffix length that needs to be ignored when calculating the consistent HASH |
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| 31 | tsdb_pagesize | INT | Page size for vnode data storage engine, in KB |
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## INS_FUNCTIONS
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## INS_FUNCTIONS
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@ -12,7 +12,15 @@ TDengine 内置了一个名为 `INFORMATION_SCHEMA` 的数据库,提供对数
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4. TDengine 在后续演进中可以灵活的添加已有 INFORMATION_SCHEMA 中表的列,而不用担心对既有业务系统造成影响
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4. TDengine 在后续演进中可以灵活的添加已有 INFORMATION_SCHEMA 中表的列,而不用担心对既有业务系统造成影响
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5. 与其他数据库系统更具互操作性。例如,Oracle 数据库用户熟悉查询 Oracle 数据字典中的表
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5. 与其他数据库系统更具互操作性。例如,Oracle 数据库用户熟悉查询 Oracle 数据字典中的表
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Note: 由于 SHOW 语句已经被开发者熟悉和广泛使用,所以它们仍然被保留。
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:::info
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- 由于 SHOW 语句已经被开发者熟悉和广泛使用,所以它们仍然被保留。
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- 系统表中的一些列可能是关键字,在查询时需要使用转义符'\`',例如查询数据库 test 有几个 VGROUP:
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```sql
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select `vgroups` from ins_databases where name = 'test';
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```
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:::
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本章将详细介绍 `INFORMATION_SCHEMA` 这个内置元数据库中的表和表结构。
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本章将详细介绍 `INFORMATION_SCHEMA` 这个内置元数据库中的表和表结构。
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@ -103,7 +111,11 @@ Note: 由于 SHOW 语句已经被开发者熟悉和广泛使用,所以它们
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| 24 | wal_retention_period | INT | WAL 的保存时长 |
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| 24 | wal_retention_period | INT | WAL 的保存时长 |
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| 25 | wal_retention_size | INT | WAL 的保存上限 |
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| 25 | wal_retention_size | INT | WAL 的保存上限 |
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| 26 | wal_roll_period | INT | wal 文件切换时长 |
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| 26 | wal_roll_period | INT | wal 文件切换时长 |
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| 27 | wal_segment_size | wal 单个文件大小 |
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| 27 | wal_segment_size | BIGINT | wal 单个文件大小 |
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| 28 | stt_trigger | SMALLINT | 表示落盘文件触发文件合并的个数 |
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| 29 | table_prefix | SMALLINT | 表示表名用于计算一致性 HASH 时需要忽略的前缀长度 |
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| 30 | table_suffix | SMALLINT | 表示表名用于计算一致性 HASH 时需要忽略的后缀长度 |
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| 31 | tsdb_pagesize | INT | 一个 VNODE 中时序数据存储引擎的页大小 |
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## INS_FUNCTIONS
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## INS_FUNCTIONS
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