使用 pdo 获取行数

get number of rows with pdo(使用 pdo 获取行数)

问题描述

我有一个简单的 pdo 准备查询:

I have a simple pdo prepared query:

$result = $db->prepare("select id, course from coursescompleted where person=:p"); 
$result ->bindParam(':p', $q, PDO::PARAM_INT);
$result->execute();
$rows = $result->fetch(PDO::FETCH_NUM);
echo $rows[0];

echo 好像返回的是记录的 ID 值，而不是查询返回的记录数?

the echo seems to be returning the ID value of the record, not the number of records returned by the query?

对此有何想法或解释?

推荐答案

PDO::FETCH_NUM: 返回一个按列号索引的数组，在结果集中返回，从第 0 列开始

PDO::FETCH_NUM: returns an array indexed by column number as returned in your result set, starting at column 0

您根本没有获取行数.

SELECT COUNT(*) FROM coursescompleted where person=:p

此查询将返回 $rows[0];

请参阅@ray 的回答.对于 InnoDB，使用 count(id) 比 count(*) 更好.

Please see @ray's answer. using count(id) is better than count(*) for InnoDB.

您可以通过以下方式从您之前的查询中获取行数.

You could get row-count in the following manner, from your earlier query.

$row_count = $result->rowCount();

但请注意:

如果关联的 PDOStatement 执行的最后一条 SQL 语句是一条 SELECT 语句，某些数据库可能会返回行数该语句返回.但是，不能保证此行为适用于所有数据库，不应依赖于可移植应用程序.

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.

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