一、优点
1、大家知道 Delphi 对 ADO 接口进行了一番包装后形成了 ADOExpress，我想 Borland 的主要目的还是想与自己的数据敏感控件相连。然而事实上数据敏感控件并不是那么耀眼，如果你希望编出来的程序稍微有点水准的话就别用那玩意；如果你很少使用数据敏感控件，那么 ADOExpress 基本上失去了其应有的作用，无数冗余的属性、虚方法，不管你用不用得到一股脑给你编译进去，也会使你的程序再大上 200K；效率么，不说了。
2、MSDN 和 VB 中的例子你可以搬过来就用。
3、关于代码重用：我给大家的例子都是以函数或过程形式，重用性不好么？
4、别说帖子太长，那你看看 DB.pas, ADODB.pas 多长？

二、基本储备
1、一些必须的单元
uses
  Variants, ComObj;

2、一些基本常数（其它查 ADODB2000.pas）：
const
  adOpenDynamic = $00000002;
  adOpenStatic = $00000003;

  adLockOptimistic = $00000003;
  adLockBatchOptimistic = $00000004;

  adStateClosed = $00000000;
  adStateOpen = $00000001;
  adStateConnecting = $00000002;
  adStateExecuting = $00000004;
  adStateFetching = $00000008;

  adUseServer = $00000002;
  adUseClient = $00000003;

  adModeReadWrite = $00000003;

  adXactCursorStability = $00001000;

  adCmdText = $00000001;
  adCmdTable = $00000002;
  adCmdStoredProc = $00000004;
  adCmdFile = $00000100;

  adAffectCurrent = $00000001;
  adAffectGroup = $00000002;
  adAffectAll = $00000003;
  adAffectAllChapters = $00000004;

3、一些基本函数和过程
//创建 Connection 对象
function CreateConnection: OleVariant;
//释放 Connection 对象；cnn 为 Connection 对象
procedure FreeConnection(var cnn: OleVariant);
//创建 Recordset 对象
function CreateRecordset: OleVariant;
//释放 Recordset 对象；rst 为 Recordset 对象
procedure FreeRecordset(var rst: OleVariant);
//创建 Command 对象
function CreateCommand: OleVariant;
//释放 Command 对象；cmd 为 Command 对象
procedure FreeCommand(var cmd: OleVariant);
//用 Connection 连接到 SQLServer 数据库；cnn 为 Connection 对象，db 数据库名，host 主机名，usr 用户名，pwd 密码
function ConnectToDB(cnn: OleVariant; const db, host, usr, pwd: string): Boolean;
//执行 SQL 语句，有返回行，无事务处理；cnn 为 Connection 对象，rst 为 Recordset 对象，sql 为 SQL 语句（可以是存储过程）
function ExecSQL(cnn, rst: OleVariant; const sql: string): Boolean;
//执行 SQL 语句，无返回行，有事务处理；cnn 为 Connection 对象，cmd 为 Command 对象，sql 为 SQL 语句（可以是存储过程）
function ExecSQLA(cnn, cmd: OleVariant; const sql: string): Boolean;

function CreateConnection: OleVariant;
begin
  try
    Result := CreateOleObject('ADODB.Connection');
    Result.CursorLocation := adUseServer;
    Result.IsolationLevel := adXactCursorStability;
    Result.Mode := adModeReadWrite;
    Result.Provider := 'SQLOLEDB.1';
  except
    if not VarIsEmpty(Result) then Result := Unassigned;
  end;
end;

procedure FreeConnection(var cnn: OleVariant);
begin
  if not VarIsEmpty(cnn) then
  begin
    if cnn.State <> adStateClosed then cnn.Close;
    cnn := Unassigned;
  end;
end;

function CreateRecordset: OleVariant;
begin
  try
    Result := CreateOleObject('ADODB.Recordset');
    Result.CacheSize := 1000;
    Result.CursorType := adOpenStatic;
    Result.CursorLocation := adUseServer;
    Result.LockType := adLockOptimistic;
  except
    if not VarIsEmpty(Result) then Result := Unassigned;
  end;
end;

procedure FreeRecordset(var rst: OleVariant);
begin
  FreeConnection(rst);
end;

function CreateCommand: OleVariant;
begin
  try
    Result := CreateOleObject('ADODB.Command');
    Result.CommandType := adCmdText;
    Result.CommandTimeout := 5;
  except
    if not VarIsEmpty(Result) then Result := Unassigned;
  end;
end;

procedure FreeCommand(var cmd: OleVariant);
begin
  if not VarIsEmpty(cmd) then cmd := Unassigned;
end;

function ConnectToDB(cnn: OleVariant; const db, host, usr, pwd: string): Boolean;
begin
  Result := not VarIsEmpty(cnn);
  if Result then
  begin
    if cnn.State <> adStateClosed then cnn.Close;
    cnn.ConnectionString :=
      'Provider=SQLOLEDB.1;Persist Security Info=True;Initial Catalog=' +
      db + ';Data Source=' + host + ';Connect Timeout=5;' +
      'Use Procedure for Prepare=1';
    try
      cnn.Open(cnn.ConnectionString, usr, pwd, -1);
    except
      Result := False;
    end;
  end;
end;

function ExecSQL(cnn, rst: OleVariant; const sql: string): Boolean;
begin
  Result := not (VarIsEmpty(cnn) or VarIsEmpty(rst)) and (cnn.State = adStateOpen);
  if Result then
  begin
    if rst.State <> adStateClosed then rst.Close;
    try
      rst.Open(sql, cnn, adOpenStatic, adLockOptimistic, adCmdText);
    except
      Result := False;
    end;
  end;
end;

function ExecSQLA(cnn, cmd: OleVariant; const sql: string): Boolean;
begin
  Result := not (VarIsEmpty(cnn) or VarIsEmpty(cmd)) and (cnn.State = adStateOpen);
  if Result then
  begin
    cnn.BeginTrans;
    try
      cmd.ActiveConnection := cnn;
      cmd.CommandText := sql;
      cmd.Prepared := True;
      cmd.Execute;
      cnn.CommitTrans;
    except
      cnn.RollbackTrans;
      Result := False;
    end;
  end;
end;

三、访问数据
1、最前 rst.MoveFirst;
2、最后 rst.MoveLast;
3、向前 rst.MovePrevious;
4、向后 rst.MoveNext;
5、取当前记录 rst.Fields[0].Value 或 rst.Fields['字段名'].Value;
6、修改当前记录 rst.Update(rst.Fields[0].Name, 某值);
7、取消修改 rst.CancelUpdate;
8、删除当前记录 rst.Delete(adAffectCurrent);
9、删除所有记录 rst.Delete(adAffectAll);
10、追加记录
  rst.AddNew;
  rst.Fields[0].Value := 值1;
  rst.Fields[1].Value := 值2;
  rst.Update;
11、刷新 rst.Refresh;
12、记录数 rst.RecordCount
15、其它方法和属性查 MSDN 或 ADO 的帮助;

四、一些例子

//变量声明
var
  cnn, rst, cmd: OleVariant;

//创建对象
procedure TForm1.FormCreate(Sender: TObject);
begin
  cnn := CreateConnection;
  rst := CreateRecordset;
  cmd := CreateCommand;
end;

//释放对象
procedure TForm1.FormDestroy(Sender: TObject);
begin
  FreeCommand(cmd);
  FreeRecordset(rst);
  FreeConnection(cnn);
end;

//连接数据库
procedure TForm1.Button1Click(Sender: TObject);
begin
  if ConnectToDB(cnn, 'mydb', '127.0.0.1', 'sa', 'ok') then
    Caption := '连接成功'
  else Caption := '连接失败';
end;

//取记录
procedure TForm1.Button2Click(Sender: TObject);
begin
  if ExecSQL(cnn, rst, 'select * from 表a') then
    Caption := VarToStr(rst.Fields['字段a'].Value);
end;

五、原生 ADO 与 Delphi ADOExpress 组件的对应关系
1、Connection <=> ADOConnection.ConnectionObject;
2、Recordset <=> ADODataSet.Recordset;
3、Command <=> ADOCommand.CommandObject;
4、? <=> ADOQuery，因为 ADOQuery 根本就不是原生 ADO 对象
5、ExecSQL <=> ADODataSet.Open;
6、ExecSQLA <=> ADOCommand.Execute;
7、有了上面几个其它的就不多说了

六、与数据库结构有关的一些函数
1、动态改变字段名称
uses ComObj;
//Access
//TableName: 表名; OldColName: 原字段名; NewColName: 新字段名;
procedure RenameField(const TableName, OldColName, NewColName: string);
var
  DB, Col: OleVariant;
begin
  DB := CreateOleObject('ADOX.Catalog');
  DB.ActiveConnection := ADOConnection1.ConnectionObject;
  Col := CreateOleObject('ADOX.Column');
  Col := DB.Tables[TableName].Columns[OldColName];
  Col.Name := NewColName;
end;

//SQLServer
procedure RenameField(const TableName, OldColName, NewColName: string);
begin
  with ADOCommand1 do
  begin
    CommandText := 'EXEC sp_rename ''' + TableName + '.' + OldColName +
      ''',''' + NewColName + ''',''COLUMN'';';
    Excute;
  end;
end;

2、取得 Access 库中的表结构
type
  TTableDef = record
    Name,
    DateCreated,
    LastUpdated,
    Description: string;
  end;

  TTableDefs = array of TTableDef;

procedure GetTableDefs(const DBName: string; out TableDefs: TTableDefs);
var
  DBEngine, DB: OleVariant;
  I: Longint;
begin
  try
    DBEngine := CreateOleObject('DAO.DBEngine.36');
    DB := DBEngine.OpenDatabase(DBName);
    SetLength(TableDefs, Longint(DB.TableDefs.Count));
    for I := Low(TableDefs) to High(TableDefs) do
    begin
      TableDefs[I].Name := DB.TableDefs[I].Name;
      TableDefs[I].DateCreated := DB.TableDefs[I].DateCreated;
      TableDefs[I].LastUpdated := DB.TableDefs[I].LastUpdated;
      try
        TableDefs[I].Description := DB.TableDefs[I].Properties['Description'].Value;
      except
        TableDefs[I].Description := '';
      end;
    end;
  finally
    DB := Unassigned;
    DBEngine := Unassigned;
  end;
end;

3、取得 Access 表中的字段结构
type
  TFieldDef = record
    Name: string;
    Types,
    Size: Longint;
    Description: string;
  end;

  TFieldDefs = array of TFieldDef;

procedure GetFieldDefs(const DBName, TableName: string; out FieldDefs: TFieldDefs);
var
  DBEngine, DB: OleVariant;
  I: Longint;
begin
  try
    DBEngine := CreateOleObject('DAO.DBEngine.36');
    DB := DBEngine.OpenDatabase(DBName);
    SetLength(FieldDefs, Longint(DB.TableDefs[TableName].Fields.Count));
    for I := Low(FieldDefs) to High(FieldDefs) do
    begin
      FieldDefs[I].Name := DB.TableDefs[TableName].Fields[I].Name;
      FieldDefs[I].Types := DB.TableDefs[TableName].Fields[I].Type;
      FieldDefs[I].Size := DB.TableDefs[TableName].Fields[I].Size;
      try
        FieldDefs[I].Description := DB.TableDefs[TableName].Fields[I].Properties['Description'].Value;
      except
        FieldDefs[I].Description := '';
      end;
    end;
  finally
    DB := Unassigned;
    DBEngine := Unassigned;
  end;
end;