問題描述

我有一個在樹結構數據中獲取路徑的函數.

I have a function for getting path in a tree structure data.

根據我在數據庫中的表，當我查詢 sub_id='root_id'

According to my table in DB, root should get no result when I query sub_id='root_id'

當我剛剛通過根時，rowCount 返回正確的結果，即 0.但是，當我從較低等級(第 3 位)傳遞一個節點時，在遞歸的末尾，即根，rowCount 返回 1?

When I just pass the root the rowCount return correct result which is 0. However when I pass a node from lower rank(3rd), in the end of the recursive which is root, rowCount return 1?

附注

我使用 Mysql 作為數據庫

I use Mysql as DB

這是我的桌子

main_id | sub_id
----------------    
    1   |    2    
    1   |    3    
    2   |    4    
    3   |    5

代碼:

$stmt = $conn->prepare("Select * from table where sub_id= ? ");  

function get_path($stmt,$node,&$map){

    $res=$stmt->execute(array($node));

    if(!$res){ throw new Exception( implode(' ',$stmt->errorInfo()),1); }

        echo $node.' found '.$stmt->rowCount().'<br>';

        if($stmt->rowCount()==0){ //root
            $map[]=$node;
        }else{

            foreach($stmt->fetchAll(PDO::FETCH_ASSOC) AS $row){
                $map[]=$node;
                $upper_node=$row['main_id'];
                get_path($stmt,$upper_node,$map);
        }
    }

}

如果我只是通過 get_path($stmt,1,$map);(根)

If I just pass get_path($stmt,1,$map); (the root)

輸出:

1 found 0

但是當我例如將 4 傳遞給它時輸出變成:

but when I for example pass 4 into it the output become:

4 found 1
2 found 1
1 found 1 <= it should found 0

為什么?

推薦答案

你不應該依賴 PDOStatement::rowCount() 來獲取受 SELECT 語句影響的行數，參見 PHP 手冊，PDOStatement::rowCount:

You shouldn't rely on PDOStatement::rowCount() to get the number of rows affected by a SELECT statement, see PHP manual, PDOStatement::rowCount:

DOStatement::rowCount() 返回受影響的行數相應的執行的最后一個 DELETE、INSERT 或 UPDATE 語句PDOStatement 對象.

DOStatement::rowCount() returns the number of rows affected by the last DELETE, INSERT, or UPDATE statement executed by the corresponding PDOStatement object.

如果關聯的 PDOStatement 執行的最后一條 SQL 語句是一條 SELECT 語句，某些數據庫可能會返回行數該語句返回.但是，不能保證此行為適用于所有數據庫，不應依賴于可移植應用程序.

If the last SQL statement executed by the associated PDOStatement was a SELECT statement, some databases may return the number of rows returned by that statement. However, this behaviour is not guaranteed for all databases and should not be relied on for portable applications.

[...]

示例 #2 對 SELECT 語句返回的行進行計數

Example #2 Counting rows returned by a SELECT statement

對于大多數數據庫，PDOStatement::rowCount() 不返回受 SELECT 語句影響的行數.相反，使用PDO::query() 發出一個 SELECT COUNT(*) 語句謂詞作為您想要的 SELECT 語句，然后使用PDOStatement::fetchColumn() 來檢索將要執行的行數被退回.然后，您的應用程序可以執行正確的操作.

For most databases, PDOStatement::rowCount() does not return the number of rows affected by a SELECT statement. Instead, use PDO::query() to issue a SELECT COUNT(*) statement with the same predicates as your intended SELECT statement, then use PDOStatement::fetchColumn() to retrieve the number of rows that will be returned. Your application can then perform the correct action.

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