Question

我正在尝试按project_id分组的每个项目从列投票中计算“是”投票。投票可以是“是”，“否”以及为布尔值的空值。我使用“喜欢”运算符。但它抛出错误this is my table

这是代码

$sql = "SELECT COUNT(vote) as count,project_id FROM tbl_vote group by   project_id where vote like '_Y'";
$result = $conn->query($sql);  if (mysqli_num_rows($result) > 0) {

while($row = mysqli_fetch_assoc($result)) {
    echo "count: " . $row["count"]. " project_id:".$row["project_id"]."    <br>";
  }
} 
else {
echo "0 results";
}

条件错误

警告：mysqli_num_rows（）期望参数1为mysqli_result，在第18行的C：\ xampp \ htdocs \ selection \ compute_sums.php中给出的布尔值''

Answer 1

您将分组依据子句放在where子句之前

$sql = "SELECT COUNT(vote) as count,project_id FROM tbl_vote where vote = 'Yes' group by   project_id";

SQL子句的顺序如下：

SELECT
    [ALL | DISTINCT | DISTINCTROW ]
      [HIGH_PRIORITY]
      [STRAIGHT_JOIN]
      [SQL_SMALL_RESULT] [SQL_BIG_RESULT] [SQL_BUFFER_RESULT]
      SQL_NO_CACHE [SQL_CALC_FOUND_ROWS]
    select_expr [, select_expr ...]
    [FROM table_references
      [PARTITION partition_list]
    [WHERE where_condition]
    [GROUP BY {col_name | expr | position}, ... [WITH ROLLUP]]
    [HAVING where_condition]
    [WINDOW window_name AS (window_spec)
        [, window_name AS (window_spec)] ...]
    [ORDER BY {col_name | expr | position}
      [ASC | DESC], ... [WITH ROLLUP]]
    [LIMIT {[offset,] row_count | row_count OFFSET offset}]
    [INTO OUTFILE 'file_name'
        [CHARACTER SET charset_name]
        export_options
      | INTO DUMPFILE 'file_name'
      | INTO var_name [, var_name]]
    [FOR {UPDATE | SHARE} [OF tbl_name [, tbl_name] ...] [NOWAIT | SKIP LOCKED] 
      | LOCK IN SHARE MODE]]

请参考：https://dev.mysql.com/doc/refman/8.0/en/select.html

选择计数错误mysqli_num_rows（）期望参数1为mysqli_result，给定布尔值

1 个答案: