我试图计算一个值（例如：1st place）在3个不同表的一列中出现的次数。
我按id合并4个表以获得所需的列，然后执行一个数组以获得所有值，然后使用array\u count\u values找出值在表中的次数。
它在很大程度上满足了我的要求，只是答案增加了一倍。当实际值只出现1次时，一旦我合并了表，每个值显示的都比它应该显示的多。
在我合并它们之前，这些是我的table
表1

| dancer_id | dancer_placement1|
|    1      |   2nd Place      |
|    1      |   1st Place      |
|    3      |   4th Place      |

表2

| dancer_id | dancer_placement3|
|    1      |   4th Place      |
|    1      |   1st Place      |
|    3      |   3rd Place      |
|    1      |   2nd Place      |

表3

| dancer_id | dancer_placement3|
|    2      |   6th Place      |
|    3      |   1st Place      |
|    1      |   3rd Place      |

当我把它们合并在一起时，看起来是这样的

| dancer_id | dancer_placement1|  dancer_placement2|  dancer_placement3|
|    1      |   2nd Place      |  4th Place        |  3rd Place        |    
|    1      |   1st Place      |  4th Place        |  3rd Place        |    
|    1      |   2nd Place      |  1st Place        |  3rd Place        |    
|    1      |   1st Place      |  1st Place        |  3rd Place        |
|    1      |   2nd Place      |  2nd Place        |  3rd Place        |
|    1      |   1st Place      |  2nd Place        |  3rd Place        |

实际上应该是这样的：

| dancer_id | dancer_placement1|  dancer_placement2|  dancer_placement3|
|    1      |   2nd Place      |  4th Place        |  3rd Place        |    
|    1      |   1st Place      |  1st Place        |  null             |    
|    1      |   null           |  2nd Place        |  null             |

如您所见，在舞者位置1中合并之前，“第一名”和“第二名”只出现一次，但合并后出现3次。
在舞者位置中，第1、第2和第4出现一次，但合并后各出现2次。
在舞者位置3中，第三个位置只出现一次，但合并后出现6次。
我认为我的sql可能有问题，因为其他一切都正常工作。
这是我的密码：

//GET ID 

if(isset($_GET['id'])) {
    $childId=$_GET['id']; 
//I MERGE MY TABLES
    $chartsql = <<<_SQL
SELECT
  dancers.id, 
  mark_cards1.dancer_placement1, 
  mark_cards2.dancer_placement2, 
  mark_cards3.dancer_placement3 
FROM dancers 
LEFT JOIN mark_cards1 ON mark_cards1.dancer_id1 = dancers.id
LEFT JOIN mark_cards2 ON mark_cards2.dancer_id2 = dancers.id 
LEFT JOIN mark_cards3 ON mark_cards3.dancer_id3 = dancers.id 
WHERE dancers.id = '$childId'
_SQL;

$pieChartRes = mysqli_query($con,$chartsql);

 //BELOEW CODE WORKS PERFECTLY FINE

     // creating an array to find values
    while ($pieChartRow=mysqli_fetch_array($pieChartRes)){
        $first[] = $pieChartRow['dancer_placement1'];
        $second[] = $pieChartRow["dancer_placement2"];
        $third[]= $pieChartRow["dancer_placement3"];

    }

   // COUNTING THE AMOUNT OF TIMES A SPECIFIC VALUE APPEARS

    $tmp = array_count_values($first);
    $count_first = $tmp["1st place"];
    $count_second = $tmp["2nd place"];
    $count_third = $tmp["3rd place"];

    $tmp2 = array_count_values($second);
    $count_first2 = $tmp2["1st place"];
    $count_second2 = $tmp2["2nd place"];
    $count_third2 = $tmp2["3rd place"];

    $tmp3 = array_count_values($third);
    $count_first3 = $tmp3["1st place"];
    $count_second3 = $tmp3["2nd place"];
    $count_third3 = $tmp3["3rd place"];

  //PRINTING NUMBER OF VALUES

    echo "number of 1st place in dancerplacement1: $count_first";
    echo "number of 1st place in dancerplacement2: $count_first2";
    echo "number of 1st place in dancerplacement3: $count_first3";

    echo "number of 2nd place in dancerplacement1: $count_second";
    echo "number of 2nd place in dancerplacement2: $count_second2";
    echo "number of 2nd place in dancerplacement3: $count_second3";

    echo "number of 3rd place in dancerplacement1: $count_third";
    echo "number of 3rd place in dancerplacement2: $count_third2";
    echo "number of 3rd place in dancerplacement3: $count_third3";

// GETTING TOTALS

    $first_total = $count_first + $count_first2 + $count_first3;
    $second_total = $count_second + $count_second2 + $count_second3;
    $third_total = $count_third + $count_third2 + $count_third3;
    echo "total for first place = $first_total";
    echo "total for second place = $second_total";
    echo "total for third place = $third_total";