Performing Scalar Queries

This tutorial describes the way in which you can execute 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 OS 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:

Declare the necessary variables.
Execute the query string.

Detailed steps

To make a scalar query, do the following:

Declare the necessary variables

Instantiate an object of the database class.
RSqlDatabase myDatabase;
Declare a literal to hold the query string
_LIT(kQueryString,"SELECT COUNT (*) FROM myTable");
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