如何處理空的sql響應？

Question

如何在sql響應爲空的情況下向此代碼添加句柄？

<?php 
$userReferrals_query = sql_query("SELECT id as id2 FROM balances WHERE email = '$address'"); 
$id2 = fetch_assoc($userReferrals_query); 


$userReferrals_query2 = sql_query("SELECT COUNT(*) AS referrals FROM balances WHERE referredby = '".$id2['id2']."'"); 
$referrals = fetch_assoc($userReferrals_query2); 
?> 

Answer 1

你可以這樣做：

if(empty($id2)){ 
//Code to handle empty response 
} 

Answer 2

fetch_assoc()回報false如果在結果沒有剩餘的行。如果您只提取1行，並且沒有匹配的行，則會在第一次調用時返回false。所以只是測試$id2是truthy還是假：

if ($id2) { 
    // do referrals query 
} 

或者你可以簡單地用一個JOIN結合這兩個查詢：

$userReferralsQuery = sql_query("SELECT COUNT(*) AS referrals 
           FROM balances AS b1 
           JOIN balances AS b2 ON b1.referred_by = b2.id 
           WHERE b2.email = '$address'";