update docs

Signed-off-by: NAnnie_wang <annie.wangli@huawei.com>

en/application-dev/database/data-persistence-by-rdb-store.md

@@ -65,6 +65,7 @@ The following table lists the APIs used for RDB data persistence. Most of the AP
          securityLevel: relationalStore.SecurityLevel.S1 // Database security level.
        };
 
+       // The current RDB store version is 3, and the table structure is EMPLOYEE (NAME, AGE, SALARY, CODES).
        const SQL_CREATE_TABLE ='CREATE TABLE IF NOT EXISTS EMPLOYEE (ID INTEGER PRIMARY KEY AUTOINCREMENT, NAME TEXT NOT NULL, AGE INTEGER, SALARY REAL, CODES BLOB)'; // SQL statement for creating a data table.
 
        relationalStore.getRdbStore(this.context, STORE_CONFIG, (err, store) => {
@@ -73,7 +74,28 @@ The following table lists the APIs used for RDB data persistence. Most of the AP
            return;
          }
          console.info(`Succeeded in getting RdbStore.`);
+
+        // When the RDB store is created, the default version is 0.
+        if (store.version == 0) {
           store.executeSql(SQL_CREATE_TABLE); // Create a data table.
+          // Set the RDB store version, which must be an integer greater than 0.
+          store.version = 3;
+        }
+
+        // If the RDB store version is not 0 and does not match the current version, upgrade or downgrade the RDB store.
+        // For example, upgrade the RDB store from version 1 to version 2.
+        if (store.version != 3 && store.version == 1) {
+          // Upgrade the RDB store from version 1 to version 2, and change the table structure from EMPLOYEE (NAME, SALARY, CODES, ADDRESS) to EMPLOYEE (NAME, AGE, SALARY, CODES, ADDRESS).
+          store.executeSql("ALTER TABLE EMPLOYEE ADD COLUMN AGE INTEGER", null);
+          store.version = 2;
+        }
+
+        // For example, upgrade the RDB store from version 2 to version 3.
+        if (store.version != 3 && store.version == 2) {
+          // Upgrade the RDB store from version 2 to version 3, and change the table structure from EMPLOYEE (NAME, AGE, SALARY, CODES, ADDRESS) to EMPLOYEE (NAME, AGE, SALARY, CODES).
+          store.executeSql("ALTER TABLE EMPLOYEE DROP COLUMN ADDRESS TEXT", null);
+          store.version = 3;
+        }
 
          // Perform operations such as adding, deleting, modifying, and querying data in the RDB store.
 
@@ -97,6 +119,7 @@ The following table lists the APIs used for RDB data persistence. Most of the AP
      securityLevel: relationalStore.SecurityLevel.S1 // Database security level.
    };
 
+   // The RDB store version is 3, and the table structure is EMPLOYEE (NAME, AGE, SALARY, CODES).
    const SQL_CREATE_TABLE ='CREATE TABLE IF NOT EXISTS EMPLOYEE (ID INTEGER PRIMARY KEY AUTOINCREMENT, NAME TEXT NOT NULL, AGE INTEGER, SALARY REAL, CODES BLOB)'; // SQL statement for creating a data table.
 
    relationalStore.getRdbStore(context, STORE_CONFIG, (err, store) => {
@@ -105,7 +128,28 @@ The following table lists the APIs used for RDB data persistence. Most of the AP
        return;
      }
      console.info(`Succeeded in getting RdbStore.`);
+
+     // When the RDB store is created, the default version is 0.
+     if (store.version == 0) {
         store.executeSql(SQL_CREATE_TABLE); // Create a data table.
+        // Set the RDB store version, which must be an integer greater than 0.
+        store.version = 3;
+     }
+
+     // If the RDB store version is not 0 and does not match the current version, upgrade or downgrade the RDB store.
+     // For example, upgrade the RDB store from version 1 to version 2.
+     if (store.version != 3 && store.version == 1) {
+        // Upgrade the RDB store from version 1 to version 2, and change the table structure from EMPLOYEE (NAME, SALARY, CODES, ADDRESS) to EMPLOYEE (NAME, AGE, SALARY, CODES, ADDRESS).
+        store.executeSql("ALTER TABLE EMPLOYEE ADD COLUMN AGE INTEGER", null);
+        store.version = 2;
+     }
+
+     // For example, upgrade the RDB store from version 2 to version 3.
+     if (store.version != 3 && store.version == 2) {
+        // Upgrade the RDB store from version 2 to version 3, and change the table structure from EMPLOYEE (NAME, AGE, SALARY, CODES, ADDRESS) to EMPLOYEE (NAME, AGE, SALARY, CODES).
+        store.executeSql("ALTER TABLE EMPLOYEE DROP COLUMN ADDRESS TEXT", null);
+        store.version = 3;
+     }
    
      // Perform operations such as adding, deleting, modifying, and querying data in the RDB store.
    
@@ -185,13 +229,22 @@ The following table lists the APIs used for RDB data persistence. Most of the AP
    ```js
    let predicates = new relationalStore.RdbPredicates('EMPLOYEE');
    predicates.equalTo('NAME', 'Rose');
-   store.query(predicates, ['ID', 'NAME', 'AGE', 'SALARY', 'CODES'], (err, resultSet) => {
+   store.query(predicates, ['ID', 'NAME', 'AGE', 'SALARY'], (err, resultSet) => {
      if (err) {
        console.error(`Failed to query data. Code:${err.code}, message:${err.message}`);
        return;
      }
-     console.info(`ResultSet column names: ${resultSet.columnNames}`);
-     console.info(`ResultSet column count: ${resultSet.columnCount}`);
+     console.info(`ResultSet column names: ${resultSet.columnNames}, column count: ${resultSet.columnCount}`);
+     // resultSet is a cursor of a data set. By default, the cursor points to the -1st record. Valid data starts from 0.
+     while (resultSet.goToNextRow()) {
+       const id = resultSet.getLong(resultSet.getColumnIndex("ID"));
+       const name = resultSet.getString(resultSet.getColumnIndex("NAME"));
+       const age = resultSet.getLong(resultSet.getColumnIndex("AGE"));
+       const salary = resultSet.getDouble(resultSet.getColumnIndex("SALARY"));
+       console.info(`id=${id}, name=${name}, age=${age}, salary=${salary}`);
+     }
+     // Release the data set memory.
+     resultSet.close();
    })
    ```
 
@@ -221,7 +274,7 @@ The following table lists the APIs used for RDB data persistence. Most of the AP
          console.info('Succeeded in deleting RdbStore.');
        });
      }
-}
+   }
    ```
 
    FA model: