sqlite - WITH子句中的准备语句导致无限循环答案

【问题标题】：sqlite - Prepared statement in WITH clause causes infinite loopsqlite - WITH子句中的准备语句导致无限循环
【发布时间】：2019-06-18 16:01:49
【问题描述】：

我有一个 PHP 脚本，它使用带有 WITH 子句的 SQLite 准备语句来打印从 2 到指定结尾的数字。当我运行它时，程序永远不会退出并输出 5 之后的数字（指定为参数）。当我运行结束固定（在 SQL 代码中为常量）而不是准备好的语句的类似程序时，它会输出预期的数字。

<?php

// Version with prepared statement

$db = new PDO("sqlite::memory:");
$s = $db->prepare("WITH RECURSIVE range(i) AS (
  SELECT 2
  UNION
  SELECT i + 1 FROM range WHERE i < :to
) select * from range
");
$s->execute(array(":to" => 5));

foreach ($s as $value)
    echo $value[0] . "\n";

<?php

// Version with constant -- working

$db = new PDO("sqlite::memory:");
$s = $db->prepare("WITH RECURSIVE range(i) AS (
  SELECT 2
  UNION
  SELECT i + 1 FROM range WHERE i < 5
) select * from range
");
$s->execute(array());

foreach ($s as $value)
    echo $value[0] . "\n";

【问题讨论】：

我认为 CTE 的递归部分是这里的罪魁祸首。不确定解决方法。

标签： sql sqlite pdo prepared-statement infinite-loop

【解决方案1】：

LIMIT 可用于限制行数。这并不适用于所有情况，但可以在我们知道行数时使用。

<?php

// Version with prepared statement and LIMIT

$db = new PDO("sqlite::memory:");
$s = $db->prepare("WITH RECURSIVE range(i) AS (
  SELECT 2
  UNION
  SELECT i + 1 FROM range WHERE i < :to
) select i from range limit :to - 1
");
$s->execute(array(":to" => 5));

foreach ($s as $value)
    echo $value[0] . "\n";

【讨论】：