A relational database (RDB) store allows you to operate local data with or without native SQL statements based on SQLite.
A relational database (RDB) store allows you to manage local data with or without native SQL statements based on SQLite.
## Available APIs
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### Creating or Deleting an RDB Store
The following table describes the APIs available for creating and deleting an RDB store.
The table below describes the APIs available for creating and deleting an RDB store.
**Table 1** APIs for creating and deleting an RDB store
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### Managing Data in an RDB Store
The RDB provides APIs for inserting, deleting, updating, and querying data in the local RDB store.
The **RDB** module provides APIs for inserting, deleting, updating, and querying data in a local RDB store.
-**Inserting data**
The RDB provides APIs for inserting data through a **ValuesBucket** in a data table. If the data is inserted, the row ID of the data inserted will be returned; otherwise, **-1** will be returned.
The **RDB** module provides APIs for inserting data through a **ValuesBucket** in a data table. If the data is inserted, the row ID of the data inserted will be returned; otherwise, **-1** will be returned.
**Table 2** API for inserting data
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| Class| API| Description|
| -------- | -------- | -------- |
| RdbStore | update(values:ValuesBucket,predicates:RdbPredicates):Promise<number> | Updates data based on the specified **RdbPredicates** object. This API uses a promise to return the result.<br>Return value: number of rows updated.<br>- **values**: data to update, which is stored in **ValuesBucket**.<br>- **predicates**: conditions for updating data.|
| RdbStore | update(values:ValuesBucket,predicates:RdbPredicates):Promise<number> | Updates data based on the specified **RdbPredicates** object. This API uses a promise to return the result.<br>Return value: number of rows updated.<br>- **values**: data to update, which is stored in **ValuesBucket**.<br>- **predicates**: conditions for updating data.|
-**Deleting data**
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| Class| API| Description|
| -------- | -------- | -------- |
| RdbStore | delete(predicates:RdbPredicates):Promise<number> | Deletes data from the RDB store based on the specified **RdbPredicates** object. This API uses a promise to return the result.<br>Return value: number of rows updated.<br>- **predicates**: conditions for deleting data.|
| RdbStore | delete(predicates:RdbPredicates):Promise<number> | Deletes data from the RDB store based on the specified **RdbPredicates** object. This API uses a promise to return the result.<br>Return value: number of rows updated.<br>- **predicates**: conditions for deleting data.|
-**Querying data**
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### Using Predicates
The RDB provides **RdbPredicates** for you to set database operation conditions.
The **RDB** module provides **RdbPredicates** for you to set database operation conditions.
The following lists common predicates. For more information about predicates, see [**RdbPredicates**](../reference/apis/js-apis-data-rdb.md#rdbpredicates).
The table below lists common predicates. For more information about predicates, see [**RdbPredicates**](../reference/apis/js-apis-data-rdb.md#rdbpredicates).
**Table 6** APIs for using RDB store predicates
| Class| API| Description|
| -------- | -------- | -------- |
| RdbPredicates | equalTo(field:string,value:ValueType):RdbPredicates | Sets an **RdbPredicates**to match the field with data type **ValueType** and value equal to the specified value.<br>- **field**: column name in the database table.<br>- **value**: value to match the **RdbPredicates**.<br>- **RdbPredicates**: **RdbPredicates** object that matches the specified field.|
| RdbPredicates | notEqualTo(field:string,value:ValueType):RdbPredicates | Sets an **RdbPredicates**to match the field with data type **ValueType** and value not equal to the specified value.<br>- **field**: column name in the database table.<br>- **value**: value to match the **RdbPredicates**.<br>- **RdbPredicates**: **RdbPredicates** object that matches the specified field.|
| RdbPredicates | or():RdbPredicates | Adds the OR condition to the **RdbPredicates**.<br>- **RdbPredicates**: **RdbPredicates** with the OR condition.|
| RdbPredicates | and():RdbPredicates | Adds the AND condition to the **RdbPredicates**.<br>- **RdbPredicates**: **RdbPredicates** with the AND condition.|
| RdbPredicates | contains(field:string,value:string):RdbPredicates | Sets an **RdbPredicates**to match a string containing the specified value.<br>- **field**: column name in the database table.<br>- **value**: value to match the **RdbPredicates**.<br>- **RdbPredicates**: **RdbPredicates** object that matches the specified field.|
| RdbPredicates | equalTo(field:string,value:ValueType):RdbPredicates | Sets an **RdbPredicates**object to match the field with data type **ValueType** and value equal to the specified value.<br>- **field**: column name in the database table.<br>- **value**: value to match the **RdbPredicates**.<br>- **RdbPredicates**: **RdbPredicates** object created.|
| RdbPredicates | notEqualTo(field:string,value:ValueType):RdbPredicates | Sets an **RdbPredicates**object to match the field with data type **ValueType** and value not equal to the specified value.<br>- **field**: column name in the database table.<br>- **value**: value to match the **RdbPredicates**.<br>- **RdbPredicates**: **RdbPredicates** object created.|
| RdbPredicates | or():RdbPredicates | Adds the OR condition to the **RdbPredicates** object.<br>- **RdbPredicates**: **RdbPredicates** with the OR condition.|
| RdbPredicates | and():RdbPredicates | Adds the AND condition to the **RdbPredicates** object.<br>- **RdbPredicates**: **RdbPredicates** with the AND condition.|
| RdbPredicates | contains(field:string,value:string):RdbPredicates | Sets an **RdbPredicates**object to match a string containing the specified value.<br>- **field**: column name in the database table.<br>- **value**: value to match the **RdbPredicates**.<br>- **RdbPredicates**: **RdbPredicates** object created.|
### Using the Result Set
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| Class| API| Description|
| -------- | -------- | -------- |
| RdbStore |off(event:'dataChange', type: SubscribeType, observer: Callback\<Array\<string>>): void;| Unregisters the observer of the specified type for the RDB store. This method uses a callback to return the result.<br>- **type**: subscription type. **SUBSCRIBE_TYPE_REMOTE** means to subscribe to remote data changes.<br>- **observer**: observer to unregister.|
| RdbStore |off(event:'dataChange', type: SubscribeType, observer: Callback\<Array\<string>>): void;| Unregisters the observer of the specified type for the RDB store. This API uses a callback to return the result.<br>- **type**: subscription type. **SUBSCRIBE_TYPE_REMOTE** means to subscribe to remote data changes.<br>- **observer**: observer to unregister.|
### Backing Up and Restoring an RDB Store
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