php - 当我使用 concat 时，Mysql 查询不起作用

Question

我不明白为什么下面的查询没有返回任何东西。如果我更改查询，那么它将返回结果。

我现在在做什么(无输出)

$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

可能是因为您在 WHERE 和 company 之间没有空格？