SQL in Delphi Headers

When developing applications in Delphi that interact with SQL databases, it is important to understand the usage of SQL headers. SQL headers are used to connect to a database, execute SQL statements, and retrieve results from the database.

Connecting to a Database

In Delphi, SQL headers are used to connect to a database. The TADOConnection component is used to establish a connection to the database. For example:

var
  conn: TADOConnection;
begin
  conn := TADOConnection.Create(nil);
  conn.ConnectionString := 'Provider=MSOLEDBSQL;Data Source=myServerAddress;Initial Catalog=myDataBase;Integrated Security=SSPI;';
  conn.LoginPrompt := False;
  conn.Connected := True;
end;

The above code creates a new instance of the TADOConnection component, sets the connection string using the specified provider, server address, database name, and security settings, and establishes the connection.

Executing SQL Statements

Once a connection is established, SQL statements can be executed using the TADOQuery component. For example:

var
  query: TADOQuery;
begin
  query := TADOQuery.Create(nil);
  query.Connection := conn;
  query.SQL.Text := 'SELECT * FROM myTable';
  query.Open;
end;

The above code creates a new instance of the TADOQuery component, sets the connection to the previously established connection, assigns the SQL statement, and opens the query to retrieve results.

Retrieving Results

To retrieve results from an executed SQL statement, the results are stored in a recordset. The recordset can then be accessed using the TADODataSet component. For example:

var
  dataset: TADODataSet;
begin
  dataset := TADODataSet.Create(nil);
  dataset.Recordset := query.Recordset;
  while not dataset.Eof do
  begin
    // Access fields using dataset.FieldByName('fieldName').AsString
    dataset.Next;
  end;
end;

The above code creates a new instance of the TADODataSet component, sets the recordset to the previously executed SQL statement, and iterates through the recordset to access the results.

SQL headers are essential components for interacting with SQL databases in Delphi. By understanding their usage, developers can more efficiently write code to interact with these databases.