diff --git a/docs-en/12-taos-sql/02-database.md b/docs-en/12-taos-sql/02-database.md index 98b75b30b3ebebb33ce1afe413554f218092bfeb..80581b2f1bc7ce9cd046c18873d3f22b6804d8cf 100644 --- a/docs-en/12-taos-sql/02-database.md +++ b/docs-en/12-taos-sql/02-database.md @@ -4,7 +4,7 @@ title: Database description: "create and drop database, show or change database parameters" --- -## Create Datable +## Create Database ``` CREATE DATABASE [IF NOT EXISTS] db_name [KEEP keep] [DAYS days] [UPDATE 1]; @@ -12,11 +12,11 @@ CREATE DATABASE [IF NOT EXISTS] db_name [KEEP keep] [DAYS days] [UPDATE 1]; :::info -1. KEEP specifies the number of days for which the data in the database to be created will be kept, the default value is 3650 days, i.e. 10 years. The data will be deleted automatically once its age exceeds this threshold. +1. KEEP specifies the number of days for which the data in the database will be retained. The default value is 3650 days, i.e. 10 years. The data will be deleted automatically once its age exceeds this threshold. 2. UPDATE specifies whether the data can be updated and how the data can be updated. - 1. UPDATE set to 0 means update operation is not allowed, the data with an existing timestamp will be dropped silently. - 2. UPDATE set to 1 means the whole row will be updated, the columns for which no value is specified will be set to NULL - 3. UPDATE set to 2 means updating a part of columns for a row is allowed, the columns for which no value is specified will be kept as no change + 1. UPDATE set to 0 means update operation is not allowed. The update for data with an existing timestamp will be discarded silently and the original record in the database will be preserved as is. + 2. UPDATE set to 1 means the whole row will be updated. The columns for which no value is specified will be set to NULL. + 3. UPDATE set to 2 means updating a subset of columns for a row is allowed. The columns for which no value is specified will be kept unchanged. 3. The maximum length of database name is 33 bytes. 4. The maximum length of a SQL statement is 65,480 bytes. 5. Below are the parameters that can be used when creating a database @@ -35,7 +35,7 @@ CREATE DATABASE [IF NOT EXISTS] db_name [KEEP keep] [DAYS days] [UPDATE 1]; - maxVgroupsPerDb: [Description](/reference/config/#maxvgroupsperdb) - comp: [Description](/reference/config/#comp) - precision: [Description](/reference/config/#precision) -6. Please note that all of the parameters mentioned in this section can be configured in configuration file `taosd.cfg` at server side and used by default, the default parameters can be overriden if they are specified in `create database` statement. +6. Please note that all of the parameters mentioned in this section are configured in configuration file `taos.cfg` on the TDengine server. If not specified in the `create database` statement, the values from taos.cfg are used by default. To override default parameters, they must be specified in the `create database` statement. ::: @@ -52,7 +52,7 @@ USE db_name; ``` :::note -This way is not applicable when using a REST connection +This way is not applicable when using a REST connection. In a REST connection the database name must be specified before a table or stable name. For e.g. to query the stable "meters" in database "test" the query would be "SELECT count(*) from test.meters" ::: @@ -63,13 +63,13 @@ DROP DATABASE [IF EXISTS] db_name; ``` :::note -All data in the database will be deleted too. This command must be used with caution. +All data in the database will be deleted too. This command must be used with extreme caution. Please follow your organization's data integrity, data backup, data security or any other applicable SOPs before using this command. ::: ## Change Database Configuration -Some examples are shown below to demonstrate how to change the configuration of a database. Please note that some configuration parameters can be changed after the database is created, but some others can't, for details of the configuration parameters of database please refer to [Configuration Parameters](/reference/config/). +Some examples are shown below to demonstrate how to change the configuration of a database. Please note that some configuration parameters can be changed after the database is created, but some cannot. For details of the configuration parameters of database please refer to [Configuration Parameters](/reference/config/). ``` ALTER DATABASE db_name COMP 2; @@ -81,7 +81,7 @@ COMP parameter specifies whether the data is compressed and how the data is comp ALTER DATABASE db_name REPLICA 2; ``` -REPLICA parameter specifies the number of replications of the database. +REPLICA parameter specifies the number of replicas of the database. ``` ALTER DATABASE db_name KEEP 365; @@ -124,4 +124,4 @@ SHOW DATABASES; SHOW CREATE DATABASE db_name; ``` -This command is useful when migrating the data from one TDengine cluster to another one. This command can be used to get the CREATE statement, which can be used in another TDengine to create the exact same database. +This command is useful when migrating the data from one TDengine cluster to another. This command can be used to get the CREATE statement, which can be used in another TDengine instance to create the exact same database.