diff -r 000000000000 -r 89d6a7a84779 Symbian3/SDK/Source/GUID-C60DAE3D-7FB9-5619-9E5D-476A430705AF.dita --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/Symbian3/SDK/Source/GUID-C60DAE3D-7FB9-5619-9E5D-476A430705AF.dita Thu Jan 21 18:18:20 2010 +0000 @@ -0,0 +1,33 @@ + + + + + +Querying a databaseThis tutorial shows you how to create a simple SQL database query.
Introduction

This tutorial shows you how to wrap a SQL query statement into an RSqlStatement object to query a database.

The SQL statement used for the tutorial is shown here:

SELECT name FROM countries WHERE population > 10

The (SELECT) results of the query will be the value in the 'name' column FROM the 'countries' table WHERE the value of the 'population' column of the same record is > the value specified.

Procedure

  1. Prepare the Statement:

    The steps to prepare a SQL statement are shown here.

    1. Set up some constants used by the SQL statement object to define the SQL query:

      _LIT(kName,"name"); +_LIT(kPopulation,"population"); +_LIT(kVal,":Value"); +_LIT(kQueryString,"SELECT name FROM countries WHERE population > :Value");

      This defines the query parameters.

    2. Instantiate the RSqlStatement SQL statement:

      RSqlStatement myStatement;

    3. Define the indices to be used in the search:

      TInt nameIndex = myStatement.ColumnIndex(kName); +TInt populationIndex = myStatement.ColumnIndex(kPopulation);

    4. Set the 32-bit integer value for the SQL parameter 'value':

      TInt parameterIndex = myStatement.ParameterIndex(kVal); +err = myStatement.BindInt(parameterIndex,10);

      The SQL parameter to which the integer is being assigned is identified by the constant kVal from:

      _LIT(kVal,":Value"); +... +...WHERE population > :Value")

      The parameter plus constant, along with other parts of the statement, are converted into:

      in SQL syntax.

    5. Prepare the statement:

      TInt err; +err = myStatement.Prepare(countriesDatabase,kQueryString);

      This creates a parameterised SQL statement executable.

  2. Run the SQL query:

    1. Search the records until a match is found:

      while((err = myStatement.Next()) == KSqlAtRow) + { + Do something with the query results + }

      Next() fires the executable SQL statement and stops at and returns the matched record.

      Do something if no results are found.

      if(err == KSqlAtEnd) + <OK - no more records>; +else + <process the error>;

  3. The query is done and you have the results. In this section we look at a simple way to do something with the results and we close the SQL statement object.

    1. Get the results of the search:

      TPtrC myData; +myData = myStatement.ColumnTextL(nameIndex); +RDebug::Print(_L("Name=%d\n"), myData);

    2. Close the SQL search statement:

      err = myStatement.Close();

      When the database search is finished the object should be closed to free up resources.

Now that you have performed a basic database query you can start thinking about more advanced querying options. The following will show you how:

  • Querying Databases: Basic

  • Reading to a buffer

  • Reading to memory

  • Reading to a data stream

SQL Overview Inserting a row into a + table Deleting rows from a + table Reading to a + buffer Reading to memory Reading to a data + stream Writing to a data + stream Scalar queries \ No newline at end of file