设有如下的关系R 和S ，且属性A 是关系R 的主码，属性D 是关系S 的主码。R <table _dj="MsoNormalTable" border="1" cellpadding="0" cellspacing="0"><tbody><tr><td valign="top" width="72">A</td><td valign="top" width="72">B</td><td valign="top" width="60">C</td></tr><tr><td valign="top" width="72">a1</td><td valign="top" width="72">b1</td><td valign="top" width="60">5</td></tr><tr><td valign="top" width="72">a2</td><td valign="top" width="72">b2</td><td valign="top" width="60">6</td></tr><tr><td valign="top" width="72">a3</td><td valign="top" width="72">b3</td><td valign="top" width="60">8</td></tr><tr><td valign="top" width="72">a4</td><td valign="top" width="72">b4</td><td valign="top" width="60">12</td></tr></tbody></table>S <table _dj="MsoNormalTable" align="left" border="1" cellpadding="0" cellspacing="0"><tbody><tr><td valign="top" width="35">D</td><td valign="top" width="36">B</td></tr><tr><td valign="top" width="35">d1</td><td valign="top" width="36">b1</td></tr><tr><td valign="top" width="35">d2</td><td valign="top" width="36">b2</td></tr><tr><td valign="top" width="35">d3</td><td valign="top" width="36">b3</td></tr><tr><td valign="top" width="35">d4</td><td valign="top" width="36">b5</td></tr></tbody></table>若关系R和S的关系代数操作的结果T如下：T <table _dj="MsoNormalTable" align="left" border="1" cellpadding="0" cellspacing="0"><tbody><tr><td valign="top" width="35">A</td><td valign="top" width="36">C</td></tr><tr><td valign="top" width="35">a1</td><td valign="top" width="36">5</td></tr><tr><td valign="top" width="35">a2</td><td valign="top" width="36">6</td></tr><tr><td valign="top" width="35">a3</td><td valign="top" width="36">8</td></tr></tbody></table>