使用LIKE语句的PHP-PDO

在使用PDO时，我有一个查询需要添加LIKE语句，但脚本失败，因为没有返回任何内容。一切都很好，直到我不得不向查询字符串中添加一个搜索项，这个搜索项将用于LIKE语句。

这是代码：

<?php
        include "connect.php";
        $catId = 0;
        $start = '';
        $lastTS = '';
        $searchItem = '';
        if(isset($_REQUEST['Category'])){
            $catId = $_REQUEST['Category'];
        }
        if(isset($_REQUEST['Start'])){
            $start = $_REQUEST['Start'];
        }
        if(isset($_REQUEST['LastTS'])){
            $lastTS = $_REQUEST['LastTS'];
        }
        if(isset($_REQUEST['SearchItem'])){
            $searchItem = $_REQUEST['SearchItem'];
        }
        if($searchItem != ''){
            $searchItem = '%' . $searchItem . '%';
        }
        if($start == 'start'){
            if($catId > 0){
                $q = $conn->prepare("SELECT t.*, u.U_FirstName, u.U_LastName, c.C_Name FROM T_Thread t INNER JOIN U_User u ON t.T_U_ID = u.U_ID INNER JOIN C_Category c ON t.T_C_ID = c.C_ID WHERE t.T_C_ID = :catId AND t.T_Name LIKE :searchItem ORDER BY t.T_ID DESC LIMIT 10");
                $q->execute(array(':catId' => $catId, ':searchItem' => $searchItem));
            }else{
                $q = $conn->prepare("SELECT t.*, u.U_FirstName, u.U_LastName, c.C_Name FROM T_Thread t INNER JOIN U_User u ON t.T_U_ID = u.U_ID INNER JOIN C_Category c ON t.T_C_ID = c.C_ID WHERE t.T_Name LIKE :searchItem ORDER BY t.T_ID DESC LIMIT 10");
                $q->execute(':searchItem' => $searchItem);
            }
        }else{
            if($catId > 0){
                $q = $conn->prepare("SELECT t.*, u.U_FirstName, u.U_LastName, c.C_Name FROM T_Thread t INNER JOIN U_User u ON t.T_U_ID = u.U_ID INNER JOIN C_Category c ON t.T_C_ID = c.C_ID WHERE t.T_C_ID = :catId AND t.T_Created > :lastTS AND t.T_Name LIKE :searchItem ORDER BY t.T_ID DESC");
                $q->execute(array(':catId' => $catId, ':lastTS' => $lastTS, ':searchItem' => $searchItem));
            }else{
                $q = $conn->prepare("SELECT t.*, u.U_FirstName, u.U_LastName, c.C_Name FROM T_Thread t INNER JOIN U_User u ON t.T_U_ID = u.U_ID INNER JOIN C_Category c ON t.T_C_ID = c.C_ID WHERE t.T_Created > :lastTS AND t.T_Name LIKE :searchItem ORDER BY t.T_ID DESC");
                $q->execute(array(':lastTS' => $lastTS, ':searchItem' => $searchItem));
            }
        }
        $q->setFetchMode(PDO::FETCH_ASSOC);
        while ($r = $q->fetch()) {
            $threads[] = $r;
        }

        $arr = array('thread' => $threads);
        echo json_encode($arr);
        $conn = null;
    ?>

更新

如果我使用这段代码，没有搜索项目，它可以很好地工作：

$q = $conn->prepare("SELECT t.*, u.U_FirstName, u.U_LastName, c.C_Name FROM T_Thread t INNER JOIN U_User u ON t.T_U_ID = u.U_ID INNER JOIN C_Category c ON t.T_C_ID = c.C_ID ORDER BY t.T_ID DESC LIMIT 10");
        $q->execute();

但当我将其用于搜索项目时，不起作用：

$q = $conn->prepare("SELECT t.*, u.U_FirstName, u.U_LastName, c.C_Name FROM T_Thread t INNER JOIN U_User u ON t.T_U_ID = u.U_ID INNER JOIN C_Category c ON t.T_C_ID = c.C_ID WHERE t.T_Name LIKE :searchItem ORDER BY t.T_ID DESC LIMIT 10");
        $q->execute(':searchItem' => $searchItem);

如果我对值进行硬编码，一切都会正常工作：

        $q = $conn->prepare("SELECT t.*, u.U_FirstName, u.U_LastName, c.C_Name FROM T_Thread t INNER JOIN U_User u ON t.T_U_ID = u.U_ID INNER JOIN C_Category c ON t.T_C_ID = c.C_ID WHERE t.T_Name LIKE '%uu%' ORDER BY t.T_ID DESC LIMIT 10");
        $q->execute();