数据库查询失败 14800007
================

**问题现象**

使用rdbStore.querySql可以获取 20 条结果，但在调用resultSet.isColumnNull时出现报错，报错信息如下：

\[nodict\]::\[PrepareStep()-sqlite\_shared\_result\_set.cpp:42\]: StoreSession BeginStepQuery fail : not select sql !
\[nodict\]::\[GetColumnIndex()-abs\_result\_set.cpp:334\]: Failed to GetAllColumnNames, ret is 14800007
\[nodict\]::\[GetColumnIndex()-napi\_result\_set.cpp:474\]: IsAtLastRow failed code:14800007 columnName:-1
\[nodict\]::\[PrepareStep()-sqlite\_shared\_result\_set.cpp:42\]: StoreSession BeginStepQuery fail : not select sql !
\[nodict\]::\[GetColumnCount()-abs\_result\_set.cpp:308\]: Failed to GetAllColumnNames, ret is 14800007
\[nodict\]::\[IsColumnNull()-napi\_result\_set.cpp:503\]: throw error: code = 14800000 , message = Inner error. Inner code is 8
\[nodict\]\[ecmascript\] Pending exception before IsMixedDebugEnabled called in line:3200, exception details as follows:
\[nodict\]Error: Inner error. Inner code is 8

代码如下：

async query( ) {
  const STORE\_CONFIG: relationalStore.StoreConfig = {
    name: 'NetMonitor.db',
    securityLevel: relationalStore.SecurityLevel.S1
  };
  let rdbStore: relationalStore.RdbStore = await relationalStore.getRdbStore(context, STORE\_CONFIG).then();
  let sql = 'SELECT \* FROM net\_monitor ORDER BY id desc LIMIT 20';
  let resultSet = await rdbStore.querySql(sql)
  let uuid = this.getString(resultSet, columnUuid)  _// report errors_
}
_/\*\*_
 _\* Retrieve the string column value of the current row in the result set._
 _\* @param resultSet_
 _\* @param columnName_
 _\* @returns_
 _\*/_
private getString(resultSet: relationalStore.ResultSet, columnName: string): string | undefined {
  let isColumnNull = resultSet.isColumnNull(resultSet.getColumnIndex(columnName));
  if (isColumnNull){
    return undefined
  } else {
    return resultSet.getString(resultSet.getColumnIndex(columnName))
  }
}

**解决措施**

isColumnNull：用于检查当前行中指定列的值是否为null。

ResultSet：返回的结果集合，用于调用关系型数据库查询接口后提供给用户。

请先转到结果集中需要查询的行，再使用isColumnNull方法。例如，使用ResultSet.goToFirstRow()转到结果集的第一行。

**参考链接**

[ResultSet](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/arkts-apis-data-relationalstore-resultset)