php - SQL Distinct 与 INNER JOIN

Question

我的选项有问题如果我在查询中嵌入DISTINCT，我就会得到value= ""。如果我删除 DISTINCT 我有 value= "1" 并且我需要这个。

 $query_result = mysqli_query($db, "SELECT DISTINCT C.name FROM Category AS C INNER JOIN MarketProduct AS MP ON C.Category_ID = MP.ID_Category WHERE MP.ID_Market ='$id'");

<select name="ID_Category">
<?php
while($row = mysqli_fetch_array($query_result)){   
?>

<option value="<?php echo $row['ID_Category'] ; ?>"><?php echo $row['name'] ; ?></option>


<?php
}
?>
</select>

Answer 1

使用GROUP BY，而不是DISTINCT。见下文:

  $query_result = mysqli_query($db, "SELECT C.name FROM Category AS C INNER JOIN MarketProduct AS MP ON C.Category_ID = MP.ID_Category WHERE MP.ID_Market ='$id' GROUP BY C.name");