# RDB Development
## When to Use
A relational database (RDB) store allows you to operate local data with or without native SQL statements based on SQLite.
## Available APIs
For details about RDB APIs, see [Relational Database](../reference/apis/js-apis-data-rdb.md).
### Creating or 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
| API| Description|
| -------- | -------- |
|getRdbStore(context: Context, config: StoreConfig, version: number, callback: AsyncCallback<RdbStore>): void| Obtains an RDB store. This API uses a callback to return the result. You can set parameters for the RDB store based on service requirements, and then call APIs to perform data operations.
- **context**: context of the application or function.
- **config**: configuration of the RDB store.
- **version**: RDB version.
- **callback**: callback invoked to return the RDB store obtained.|
|getRdbStore(context: Context, config: StoreConfig, version: number): Promise<RdbStore> | Obtains an RDB store. This API uses a promise to return the result. You can set parameters for the RDB store based on service requirements, and then call APIs to perform data operations.
- **context**: context of the application or function.
- **config**: configuration of the RDB store.
- **version**: RDB version.|
|deleteRdbStore(context: Context, name: string, callback: AsyncCallback<void> ): void | Deletes an RDB store. This API uses a callback to return the result.
- **context**: context of the application or function.
- **name**: RDB store to delete.
- **callback**: callback invoked to return the result.|
| deleteRdbStore(context: Context, name: string): Promise<void> | Deletes an RDB store. This API uses a promise to return the result.
- **context**: context of the application or function.
- **name**: RDB store to delete.|
### Managing Data in an RDB Store
The RDB provides APIs for inserting, deleting, updating, and querying data in the 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.
**Table 2** APIs for inserting data
| Class| API| Description|
| -------- | -------- | -------- |
| RdbStore | insert(table: string, values: ValuesBucket, callback: AsyncCallback<number>):void | Inserts a row of data into a table. This API uses a callback to return the result.
- **table**: name of the target table.
- **values**: data to be inserted into the table.
- **callback**: callback invoked to return the result. If the operation is successful, the row ID will be returned. Otherwise, **-1** will be returned.|
| RdbStore | insert(table: string, values: ValuesBucket): Promise<number> | Inserts a row of data into a table. This API uses a promise to return the result.
- **table**: name of the target table.
- **values**: data to be inserted into the table.|
- **Updating data**
Call the **update()** method to pass new data and specify the update conditions by using **RdbPredicates**. If the data is updated, the number of rows of the updated data will be returned; otherwise, **0** will be returned.
**Table 3** APIs for updating data
| Class| API| Description|
| -------- | -------- | -------- |
| RdbStore | update(values: ValuesBucket, predicates: RdbPredicates, callback: AsyncCallback<number>):void | Updates data in the RDB store based on the specified **RdbPredicates** object. This API uses a callback to return the result.
- **values**: data to update, which is stored in a **ValuesBucket**.
- **predicates**: conditions for updating data.
- **callback**: callback invoked to return the number of rows updated.|
| RdbStore | update(values: ValuesBucket, predicates: RdbPredicates): Promise<number> | Updates data in the RDB store based on the specified **RdbPredicates** object. This API uses a promise to return the result.
- **values**: data to update, which is stored in a **ValuesBucket**.
- **predicates**: conditions for updating data.|
- **Deleting data**
Call the **delete()** method to delete data meeting the conditions specified by **RdbPredicates**. If the data is deleted, the number of rows of the deleted data will be returned; otherwise, **0** will be returned.
**Table 4** APIs for deleting data
| Class| API| Description|
| -------- | -------- | -------- |
| RdbStore | delete(predicates: RdbPredicates, callback: AsyncCallback<number>):void | Deletes data from the RDB store based on the specified **RdbPredicates** object. This API uses an asynchronous callback to return the result.
- **predicates**: conditions for deleting data.
- **callback**: callback invoked to return the number of rows updated.|
| 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.
- **predicates**: conditions for deleting data.|
- **Querying data**
You can query data in an RDB store in either of the following ways:
- Call the **query()** method to query data based on the predicates, without passing any SQL statement.
- Run the native SQL statement.
**Table 5** APIs for querying data
| Class| API| Description|
| -------- | -------- | -------- |
| RdbStore | query(predicates: RdbPredicates, columns: Array<string>, callback: AsyncCallback<ResultSet>): void | Queries data in the RDB store based on the specified **RdbPredicates** object. This API uses a callback to return the result.
- **predicates**: conditions for querying data.
- **columns**: columns to query. If this parameter is not specified, the query applies to all columns.
- **callback**: callback invoked to return the result. If the operation is successful, a **ResultSet** object will be returned.|
| RdbStore | query(predicates: RdbPredicates, columns?: Array<string>): Promise<ResultSet> | Queries data in the RDB store based on the specified **RdbPredicates** object. This API uses a promise to return the result.
- **predicates**: conditions for querying data.
- **columns**: columns to query. If this parameter is not specified, the query applies to all columns.|
| RdbStore | querySql(sql: string, bindArgs: Array<ValueType>, callback: AsyncCallback<ResultSet>):void | Queries data in the RDB store using the specified SQL statement. This API uses a callback to return the result.
- **sql**: SQL statement.
- **bindArgs**: arguments in the SQL statement.
- **callback**: callback invoked to return the result. If the operation is successful, a **ResultSet** object will be returned.|
| RdbStore | querySql(sql: string, bindArgs?: Array<ValueType>):Promise<ResultSet> | Queries data in the RDB store using the specified SQL statement. This API uses a promise to return the result.
- **sql**: SQL statement.
- **bindArgs**: arguments in the SQL statement.|
### Using Predicates
The RDB provides **RdbPredicates** for you to set database operation conditions.
**Table 6** APIs for using RDB store predicates
| Class| API| Description|
| -------- | -------- | -------- |
| RdbPredicates |inDevices(devices: Array\): RdbPredicates | Specifies remote devices on the network with RDB stores to be synchronized.
- **devices**: IDs of the remote devices on the network.
- **RdbPredicates**: returns a **RdbPredicates** object that matches the specified field.|
| RdbPredicates |inAllDevices(): RdbPredicates | Connects to all remote devices on the network with RDB stores to be synchronized.
- **RdbPredicates**: returns a **RdbPredicates** object that matches the specified field.|
| RdbPredicates | equalTo(field: string, value: ValueType): RdbPredicates | Sets the **RdbPredicates** to match the field with data type **ValueType** and value equal to the specified value.
- **field**: column name in the database table.
- **value**: value specified.
- **RdbPredicates**: returns a **RdbPredicates** object that matches the specified field.|
| RdbPredicates | notEqualTo(field: string, value: ValueType): RdbPredicates | Sets the **RdbPredicates** to match the field with data type **ValueType** and value not equal to the specified value.
- **field**: column name in the database table.
- **value**: value specified.
- **RdbPredicates**: returns a **RdbPredicates** object that matches the specified field.|
| RdbPredicates | beginWrap(): RdbPredicates | Adds a left parenthesis to the **RdbPredicates**.
- **RdbPredicates**: returns a **RdbPredicates** with a left parenthesis.|
| RdbPredicates | endWrap(): RdbPredicates | Adds a right parenthesis to the **RdbPredicates**.
- **RdbPredicates**: returns a **RdbPredicates** with a right parenthesis.|
| RdbPredicates | or(): RdbPredicates | Adds the OR condition to the **RdbPredicates**.
- **RdbPredicates**: returns a **RdbPredicates** with the OR condition.|
| RdbPredicates | and(): RdbPredicates | Adds the AND condition to the **RdbPredicates**.
- **RdbPredicates**: returns a **RdbPredicates** with the AND condition.|
| RdbPredicates | contains(field: string, value: string): RdbPredicates | Sets the **RdbPredicates** to match a string containing the specified value.
- **field**: column name in the database table.
- **value**: value specified.
- **RdbPredicates**: returns a **RdbPredicates** object that matches the specified string.|
| RdbPredicates | beginsWith(field: string, value: string): RdbPredicates | Sets the **RdbPredicates** to match a string that starts with the specified value.
- **field**: column name in the database table.
- **value**: value specified.
- **RdbPredicates**: returns a **RdbPredicates** object that matches the specified field.|
| RdbPredicates | endsWith(field: string, value: string): RdbPredicates | Sets the **RdbPredicates** to match a string that ends with the specified value.
- **field**: column name in the database table.
- **value**: value specified.
- **RdbPredicates**: returns a **RdbPredicates** object that matches the specified field.|
| RdbPredicates | isNull(field: string): RdbPredicates | Sets the **RdbPredicates** to match the field whose value is null.
- **field**: column name in the database table.
- **RdbPredicates**: returns a **RdbPredicates** object that matches the specified field.|
| RdbPredicates | isNotNull(field: string): RdbPredicates | Sets the **RdbPredicates** to match the field whose value is not null.
- **field**: column name in the database table.
- **RdbPredicates**: returns a **RdbPredicates** object that matches the specified field.|
| RdbPredicates | like(field: string, value: string): RdbPredicates | Sets the **RdbPredicates** to match a string that is similar to the specified value.
- **field**: column name in the database table.
- **value**: value specified.
- **RdbPredicates**: returns a **RdbPredicates** object that matches the specified field.|
| RdbPredicates | glob(field: string, value: string): RdbPredicates | Sets the **RdbPredicates** to match the specified string.
- **field**: column name in the database table.
- **value**: value specified.
- **RdbPredicates**: returns a **RdbPredicates** object that matches the specified field.|
| RdbPredicates | between(field: string, low: ValueType, high: ValueType): RdbPredicates | Sets the **RdbPredicates** to match the field with data type **ValueType** and value within the specified range.
- **field**: column name in the database table.
- **low**: minimum value that matches the **RdbPredicates**.
- **high**: maximum value that matches the **RdbPredicates**.
- **RdbPredicates**: returns a **RdbPredicates** object that matches the specified field.|
| RdbPredicates | notBetween(field: string, low: ValueType, high: ValueType): RdbPredicates | Sets the **RdbPredicates** to match the field with data type **ValueType** and value out of the specified range.
- **field**: column name in the database table.
- **low**: minimum value that matches the **RdbPredicates**.
- **high**: maximum value that matches the **RdbPredicates**.
- **RdbPredicates**: returns a **RdbPredicates** object that matches the specified field.|
| RdbPredicates | greaterThan(field: string, value: ValueType): RdbPredicatesgr | Sets the **RdbPredicates** to match the field with data type **ValueType** and value greater than the specified value.
- **field**: column name in the database table.
- **value**: value specified.
- **RdbPredicates**: returns a **RdbPredicates** object that matches the specified field.|
| RdbPredicates | lessThan(field: string, value: ValueType): RdbPredicates | Sets the **RdbPredicates** to match the field with data type **ValueType** and value less than the specified value.
- **field**: column name in the database table.
- **value**: value specified.
- **RdbPredicates**: returns a **RdbPredicates** object that matches the specified field.|
| RdbPredicates | greaterThanOrEqualTo(field: string, value: ValueType): RdbPredicates | Sets the **RdbPredicates** to match the field with data type **ValueType** and value greater than or equal to the specified value.
- **field**: column name in the database table.
- **value**: value specified.
- **RdbPredicates**: returns a **RdbPredicates** object that matches the specified field.|
| RdbPredicates | lessThanOrEqualTo(field: string, value: ValueType): RdbPredicates | Sets the **RdbPredicates** to match the field with data type **ValueType** and value less than or equal to the specified value.
- **field**: column name in the database table.
- **value**: value specified.
- **RdbPredicates**: returns a **RdbPredicates** object that matches the specified field.|
| RdbPredicates | orderByAsc(field: string): RdbPredicates | Sets the **RdbPredicates** to match the column with values sorted in ascending order.
- **field**: column name in the database table.
- **RdbPredicates**: returns a **RdbPredicates** object that matches the specified field.|
| RdbPredicates | orderByDesc(field: string): RdbPredicates | Sets the **RdbPredicates** to match the column with values sorted in descending order.
- **field**: column name in the database table.
- **RdbPredicates**: returns a **RdbPredicates** object that matches the specified field.|
| RdbPredicates | distinct(): RdbPredicates | Sets the **RdbPredicates** to filter out duplicate records.
- **RdbPredicates**: returns a **RdbPredicates** object that can filter out duplicate records.|
| RdbPredicates | limitAs(value: number): RdbPredicates | Sets the **RdbPredicates** to specify the maximum number of records.
- **value**: maximum number of records.
- **RdbPredicates**: returns a **RdbPredicates** object that can be used to set the maximum number of records.|
| RdbPredicates | offsetAs(rowOffset: number): RdbPredicates | Sets the **RdbPredicates** to specify the start position of the returned result.
- **rowOffset**: start position of the returned result. The value is a positive integer.
- **RdbPredicates**: returns a **RdbPredicates** object that specifies the start position of the returned result.|
| RdbPredicates | groupBy(fields: Array<string>): RdbPredicates | Sets the **RdbPredicates** to group rows that have the same value into summary rows.
- **fields**: names of the columns grouped for querying data.
- **RdbPredicates**: returns a **RdbPredicates** object that groups rows with the same value.|
| RdbPredicates | indexedBy(indexName: string): RdbPredicates | Sets the **RdbPredicates** to specify the index column.
- **indexName**: name of the index column.
- **RdbPredicates**: returns a **RdbPredicates** object that specifies the index column.|
| RdbPredicates | in(field: string, value: Array<ValueType>): RdbPredicates | Sets the **RdbPredicates** to match the field with data type **Array<ValueType>** and value within the specified range.
- **field**: column name in the database table.
- **value**: array of **ValueType** to match.
- **RdbPredicates**: returns a **RdbPredicates** object that matches the specified field.|
| RdbPredicates | notIn(field: string, value: Array<ValueType>): RdbPredicates | Sets the **RdbPredicates** to match the field with data type **Array<ValueType>** and value out of the specified range.
- **field**: column name in the database table.
- **value**: array of **ValueType** to match.
- **RdbPredicates**: returns a **RdbPredicates** object that matches the specified field.|
### Using the Result Set
A result set can be regarded as a row of data in the queried results. It allows you to traverse and access the data you have queried. The following table describes the external APIs of **ResultSet**.
> **NOTICE**
> After a result set is used, you must call the **close()** method to close it explicitly.
**Table 7** APIs for using the result set
| Class| API| Description|
| -------- | -------- | -------- |
| ResultSet | goTo(offset:number): boolean | Moves the result set forwards or backwards by the specified offset relative to its current position.|
| ResultSet | goToRow(position: number): boolean | Moves the result set to the specified row.|
| ResultSet | goToNextRow(): boolean | Moves the result set to the next row.|
| ResultSet | goToPreviousRow(): boolean | Moves the result set to the previous row.|
| ResultSet | getColumnIndex(columnName: string): number | Obtains the column index based on the specified column name.|
| ResultSet | getColumnName(columnIndex: number): string | Obtains the column name based on the specified column index.|
| ResultSet | goToFirstRow(): boolean | Checks whether the result set is located in the first row.|
| ResultSet | goToLastRow(): boolean | Checks whether the result set is located in the last row.|
| ResultSet | getString(columnIndex: number): string | Obtains the value in the specified column of the current row, in a string.|
| ResultSet | getBlob(columnIndex: number): Uint8Array | Obtains the values in the specified column of the current row, in a byte array.|
| ResultSet | getDouble(columnIndex: number): number | Obtains the values in the specified column of the current row, in double.|
| ResultSet | isColumnNull(columnIndex: number): boolean | Checks whether the value in the specified column of the current row is null.|
| ResultSet | close(): void | Closes the result set.|
### Setting Distributed Tables
>**CAUTION**
ohos.permission.DISTRIBUTED_DATASYNC is required for using the **setDistributedTables**, **obtainDistributedTableName**, **sync**, **on**, and **off** APIs of **RdbStore**.
**Setting Distributed Tables**
**Table 8** APIs for setting distributed tables
| Class| API| Description|
| -------- | -------- | -------- |
| RdbStore | setDistributedTables(tables: Array\, callback: AsyncCallback\): void | Sets a list of distributed tables. This API uses a callback to return the result.
- **tables**: names of the distributed tables to set.
- **callback**: callback invoked to return the result.|
| RdbStore | setDistributedTables(tables: Array\): Promise\ | Sets a list of distributed tables. This API uses a promise to return the result.
- **tables**: names of the distributed tables to set.|
**Obtaining the Distributed Table Name for a Remote Device**
You can obtain the distributed table name for a remote device based on the local table name. The distributed table name can be used to query the RDB store of the remote device.
**Table 9** APIs for obtaining the distributed table name of a remote device
| Class| API| Description|
| -------- | -------- | -------- |
| RdbStore | obtainDistributedTableName(device: string, table: string, callback: AsyncCallback\): void | Obtains the distributed table name for a remote device based on the local table name. The distributed table name is required when the database of a remote device is queried. This API uses an asynchronous callback to return the result.
- **device**: remote device.
- **table**: local table name.
- **callback**: callback used to return the result. If the operation is successful, the distributed table name of the remote device will be returned. |
| RdbStore | obtainDistributedTableName(device: string, table: string): Promise\ | Obtains the distributed table name for a remote device based on the local table name. The distributed table name is used to query the RDB store of the remote device. This API uses a promise to return the result.
- **device**: remote device.
- **table**: local table name.|
**Synchronizing Data Between Devices**
**Table 10** APIs for synchronizing data between devices
| Class| API| Description|
| -------- | -------- | -------- |
| RdbStore | sync(mode: SyncMode, predicates: RdbPredicates, callback: AsyncCallback\>): void | Synchronizes data between devices. This API uses a callback to return the result.
- **mode**: data synchronization mode. **SYNC_MODE_PUSH** means to push data from the local device to a remote device. **SYNC_MODE_PULL** means to pull data from a remote device to the local device.
- **predicates**: data and devices to be synchronized.
- **callback**: callback invoked to return the result. In the result, **string** indicates the device ID, and **number** indicates the synchronization status of each device. The value **0** indicates a success, and other values indicate a failure.|
| RdbStore | sync(mode: SyncMode, predicates: RdbPredicates): Promise\> | Synchronizes data between devices. This API uses a promise to return the result.
- **mode**: data synchronization mode. **SYNC_MODE_PUSH** means to push data from the local device to a remote device. **SYNC_MODE_PULL** means to pull data from a remote device to the local device.
- **predicates**: data and devices to be synchronized. |
**Registering an RDB Store Observer**
**Table 11** API for registering an observer
| Class| API| Description|
| -------- | -------- | -------- |
| RdbStore |on(event: 'dataChange', type: SubscribeType, observer: Callback\>): void| Registers an observer for this RDB store to subscribe to distributed data changes. When data in the RDB store changes, a callback will be invoked to return the data changes.
- **type**: subscription type. **SUBSCRIBE_TYPE_REMOTE** means to subscribe to remote data changes.
- **observer**: observer that listens for data changes in the RDB store.|
**Unregistering an RDB Store Observer**
**Table 12** API for unregistering an observer
| Class| API| Description|
| -------- | -------- | -------- |
| RdbStore |off(event:'dataChange', type: SubscribeType, observer: Callback\>): void;| Unregisters the observer of the specified type for the RDB store. This API uses a callback to return the result.
- **type**: subscription type. **SUBSCRIBE_TYPE_REMOTE** means to subscribe to remote data changes.
- **observer**: observer to unregister.|
### Backing Up and Restore an RDB Store
**Backing Up an RDB Store**
**Table 13** APIs for backing up an RDB store
| Class| API| Description|
| -------- | -------- | -------- |
| RdbStore |backup(destName:string, callback: AsyncCallback<void>):void| Backs up the RDB store with the specified name. This API uses an asynchronous callback to return the result.
- **destName**: name of the RDB backup file.
- **callback**: callback invoked to return the result.|
| RdbStore |backup(destName:string): Promise<void>| Backs up the RDB store with the specified name. This API uses a promise to return the result.
- **destName**: name of the RDB backup file.|
**Restoring an RDB Store**
**Table 14** APIs for restoring an RDB store
| Class| API| Description|
| -------- | -------- | -------- |
| RdbStore |restore(srcName:string, callback: AsyncCallback<void>):void| Restores an RDB store using the specified backup file. This API uses an asynchronous callback to return the result.
- **srcName**: name of the RDB backup file.
- **callback**: callback invoked to return the result.|
| RdbStore |restore(srcName:string): Promise<void>| Restores an RDB store using the specified backup file. This API uses a promise to return the result.
- **srcName**: name of the RDB backup file.|
## How to Develop
1. Create an RDB store.
(1) Configure the RDB store attributes, including the RDB store name, storage mode, and whether read-only mode is used.
(2) Initialize the table structure and related data in the RDB store.
(3) Create an RDB store.
The sample code is as follows:
```js
import data_rdb from '@ohos.data.rdb'
const CREATE_TABLE_TEST = "CREATE TABLE IF NOT EXISTS test (" + "id INTEGER PRIMARY KEY AUTOINCREMENT, " + "name TEXT NOT NULL, " + "age INTEGER, " + "salary REAL, " + "blobType BLOB)";
const STORE_CONFIG = {name: "rdbstore.db",}
data_rdb.getRdbStore(this.context, STORE_CONFIG, 1, function (err, rdbStore) {
rdbStore.executeSql(CREATE_TABLE_TEST)
console.info('create table done.')
})
```
2. Insert data.
(1) Create a **ValuesBucket** to store the data you need to insert.
(2) Call the **insert()** method to insert data into the RDB store.
The sample code is as follows:
```js
var u8 = new Uint8Array([1, 2, 3])
const valueBucket = {"name": "Tom", "age": 18, "salary": 100.5, "blobType": u8,}
let insertPromise = rdbStore.insert("test", valueBucket)
```
3. Query data.
(1) Create an **RdbPredicates** object to specify query conditions.
(2) Call the **query()** API to query data.
(3) Call the **resultSet()** API to obtain the result.
The sample code is as follows:
```js
let predicates = new data_rdb.RdbPredicates("test");
predicates.equalTo("name", "Tom")
let promisequery = rdbStore.query(predicates)
promisequery.then((resultSet) => {
resultSet.goToFirstRow()
const id = resultSet.getLong(resultSet.getColumnIndex("id"))
const name = resultSet.getString(resultSet.getColumnIndex("name"))
const age = resultSet.getLong(resultSet.getColumnIndex("age"))
const salary = resultSet.getDouble(resultSet.getColumnIndex("salary"))
const blobType = resultSet.getBlob(resultSet.getColumnIndex("blobType"))
resultSet.close()
})
```
4. Set the distributed tables to be synchronized.
(1) Add the following permission to the permission configuration file:
```js
"requestPermissions":
{
"name": "ohos.permission.DISTRIBUTED_DATASYNC"
}
```
(2) Obtain the required permissions.
(3) Set the distributed tables.
(4) Check whether the setting is successful.
The sample code is as follows:
```js
let context = featureAbility.getContext();
context.requestPermissionsFromUser(['ohos.permission.DISTRIBUTED_DATASYNC'], 666, function (result) {
console.info(`result.requestCode=${result.requestCode}`)
})
let promise = rdbStore.setDistributedTables(["test"])
promise.then(() => {
console.info("setDistributedTables success.")
}).catch((err) => {
console.info("setDistributedTables failed.")
})
```
5. Synchronize data across devices.
(1) Construct an **RdbPredicates** object to specify remote devices within the network to be synchronized.
(2) Call **rdbStore.sync()** to synchronize data.
(3) Check whether the data synchronization is successful.
The sample code is as follows:
```js
let predicate = new data_rdb.RdbPredicates('test')
predicate.inDevices(['12345678abcde'])
let promise = rdbStore.sync(data_rdb.SyncMode.SYNC_MODE_PUSH, predicate)
promise.then((result) => {
console.log('sync done.')
for (let i = 0; i < result.length; i++) {
console.log('device=' + result[i][0] + ' status=' + result[i][1])
}
}).catch((err) => {
console.log('sync failed')
})
```
6. Subscribe to distributed data.
(1) Register an observer to listen for distributed data changes.
(2) When data in the RDB store changes, a callback will be invoked to return the data changes.
The sample code is as follows:
```js
function storeObserver(devices) {
for (let i = 0; i < devices.length; i++) {
console.log('device=' + device[i] + ' data changed')
}
}
try {
rdbStore.on('dataChange', data_rdb.SubscribeType.SUBSCRIBE_TYPE_REMOTE, storeObserver)
} catch (err) {
console.log('register observer failed')
}
```
7. Query data across devices.
(1) Obtain the distributed table name for a remote device based on the local table name.
(2) Call the resultSet() API to obtain the result.
The sample code is as follows:
```js
let tableName = rdbStore.obtainDistributedTableName(deviceId, "test");
let resultSet = rdbStore.querySql("SELECT * FROM " + tableName)
```
8. Back up and restore an RDB store.
(1) Back up the current RDB store.
(2) Restore the RDB store using the backup file.
The sample code is as follows:
```js
let promiseBackup = rdbStore.backup("dbBackup.db")
promiseBackup.then(()=>{
console.info('Backup success.')
}).catch((err)=>{
console.info('Backup failed, err: ' + err)
})
```
```js
let promiseRestore = rdbStore.restore("dbBackup.db")
promiseRestore.then(()=>{
console.info('Restore success.')
}).catch((err)=>{
console.info('Restore failed, err: ' + err)
})
```
## Samples
The following samples are provided for you to better understand the RDB development:
- [`Rdb`: eTS RDB (API8)](https://gitee.com/openharmony/app_samples/tree/master/data/Rdb)
- [`DistributedRdb`: eTS Distributed Relational Database (API8)](https://gitee.com/openharmony/app_samples/tree/master/data/DistributedRdb)
- [Relational Database](https://gitee.com/openharmony/codelabs/tree/master/Data/JSRelationshipData)