Question

我不明白为什么以下查询不会返回任何内容。如果我更改了查询，那么它会返回结果。

我现在在做什么（没有输出）

$msg =  array();
$getSearch = "SELECT contact_details . * , company.company_name, users.nickname FROM contact_details LEFT JOIN users ON users.user_id = contact_details.user_id LEFT JOIN company ON company.cid = contact_details.cid WHERE";  

if(!empty($ad_company)){
    $getSearch .= "company.company_name LIKE '$ad_company%' ";
}     

$getSearch =  mysql_query($getSearch);  
while($searchResult =  mysql_fetch_array($getSearch)){
$msg[] = $company = $searchResult['company_name'] . "<br/>";
}
echo  json_encode($msg);

更改代码（工作）

$msg =  array();
$getSearch = "SELECT contact_details . * , company.company_name, users.nickname FROM contact_details LEFT JOIN users ON users.user_id = contact_details.user_id LEFT JOIN company ON company.cid = contact_details.cid WHERE company.company_name LIKE '$ad_company%'"; 

//$msg[] = empty($ad_company) ? "empty company" : "not empty company"; //for checking and field has value

/*if(!empty($ad_company)){
    $getSearch .= "company.company_name LIKE '$ad_company%' ";
}*/         

$getSearch =  mysql_query($getSearch);

while($searchResult =  mysql_fetch_array($getSearch)){
$msg[] = $company = $searchResult['company_name'] . "<br/>";
}
echo  json_encode($msg);

Answer 1

也许是因为你在WHERE和公司之间没有空间？

Answer 2

试试这个

作为Mitja的回答，你错过了WHERE和公司之间的空间

$getSearch = "SELECT contact_details . * , company.company_name, users.nickname 
              FROM contact_details 
              LEFT JOIN users ON users.user_id = contact_details.user_id 
              LEFT JOIN company ON company.cid = contact_details.cid ";  

if(!empty($ad_company)){
    $getSearch .= " WHERE company.company_name LIKE '$ad_company%' ";
}

<强> EDITED

$getSearch = "SELECT contact_details . * , company.company_name, users.nickname 
              FROM contact_details 
              LEFT JOIN users ON users.user_id = contact_details.user_id 
              LEFT JOIN company ON company.cid = contact_details.cid
              WHERE 1=1 ";  

if(!empty($ad_company)){
    $getSearch .= " AND company.company_name LIKE '$ad_company%' ";
}

Answer 3

我已从您的$ getSearch查询中删除了WHERE，并将其添加到我们要附加的

中

 $getSearch = "SELECT contact_details . * , company.company_name, users.nickname FROM contact_details LEFT JOIN users ON users.user_id = contact_details.user_id LEFT JOIN company ON company.cid = contact_details.cid";  

if(!empty($ad_company)){
    $getSearch .= " WHERE company.company_name LIKE '$ad_company%' ";
}

将来如果你遇到这样的问题总是尝试在用db查询之前只打印sql查询..这样你就会看到你的查询是否正确

当我使用concat时，Mysql查询无法正常工作

3 个答案: