Use the properties and methods of SQL to specify the query that should be executed on the database server. If SQL is a SELECT statement, the query executes the statement when you call Open or set the Active property to true. If the statement does not return a result set, call the ExecSQL method to execute the statement. 

When you set the SQL property, TSQLQuery checks the statement for parameters and initializes the Params property to reflect any parameters in the statement. You can subsequently use the Params property to adjust the datatype of any parameters and supply values for the parameters. 

At design-time, edit the SQL statement using the property editor that appears when you click the ellipsis button for the property in the Object Inspector. At runtime, use properties and methods of TStrings to clear the current contents, add new contents, or to modify existing contents: 

SQLQuery1.SQL.Clear;

SQLQuery1.SQL.Add('SELECT ' + Edit1.Text + ' FROM ' + Edit2.Text);
if Length(Edit3.Text) <> 0 then

SQLQuery1.SQL.Add('ORDER BY ' + Edit3.Text) 

SQLQuery1->SQL->Clear();

SQLQuery1->SQL->Add("SELECT " + Edit1->Text + " FROM " + Edit2.Text);
if (!Edit3->Text->IsEmpty())

SQLQuery1->SQL->Add("ORDER BY " + Edit3.Text); 

You can also use the methods of SQL to load a query from a file.

Add 

Active 

Open 

ExecSQL 

Params 

Text 

Representing the Results of a Query 

Specifying the Command to Execute