Performing Scalar Queries

Introduction

A scalar query is a SELECT statement which refers to several data fields and returns a single result, for example, a COUNT query on a database column. This gives the number of records in the database. Symbian platform provides a class TSqlScalarFullSelectQuery , for making scalar queries. This is more efficient than the RSqlStatement class.

Basic procedure

The high level steps to perform scalar queries are shown here:

1. Declare the necessary variables.

2. Execute the query string.

Detailed steps

To make a scalar query, do the following:

Declare the necessary variables

1. Instantiate an object of the database class.

            
             
            
            RSqlDatabase myDatabase;
           

2. Declare a literal to hold the query string

            
             
            
            _LIT(kQueryString,"SELECT COUNT (*) FROM myTable");
           

3. Instantiate an object of the TSqlScalarFullSelectQuery class. This class has a peculiar feature of instantiating an instance of it with a parameter that refers to the database to be queried. The class supplies a number of functions taking SELECT statements as parameters.

            
             
            
            TSqlScalarFullSelectQuery myFullSelectQuery(myDatabase);
           

Execute the query

Execute the query

       TInt recCount = myFullSelectQuery.SelectIntL(kQueryString));
      

See also

Querying a Database

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

Performing Scalar Queries - This document