arrays - 如何将 GROUP_CONCAT 转换为数组

Question

如何将 install_amt 转换为逗号分隔数组

 $select = mysql_query("SELECT ac_no,cust_name,install_amt,GROUP_CONCAT(install_amt) FROM ankali_slabpay  WHERE agent_id=$agent_id GROUP BY ac_no");
    $a=array();
    while($row1 = mysql_fetch_assoc($select)){
    $installment = $row1['GROUP_CONCAT(install_amt)'];
    $a=explode(",",$installamt);