mysql或无法给出所需的结果

Question

请参考下图中的2个表格：

代码：     

$query41 = "SELECT  p.message FROM friendship f
JOIN messageslive p
ON p.username = f.frenusername OR p.username = f.username
WHERE f.username = '{$username1}' OR f.frenusername = '{$username1}'
ORDER BY
p.id DESC
LIMIT 16";
$result41 = mysql_query($query41,$connection) or die (mysql_error());
confirm_query($result41);
while($msginfo = mysql_fetch_array($result41)){
        $msg = $msginfo['message'];
        echo $msg . "<br/>";
}

输出：

live
sss
ssa
ddd
asa
(dance2)
asaaa
ssa
(bluek2)
(bluek2)
(bluek2)
(bluek2)
(bluek2)
(bluek2)
(bluek2)
(bluek2)

问题：为什么输出显示重复(bluek2)？如何修复bug？我想显示由zac1987和zac1987的朋友发布的最新16条帖子。预期输出应与表messagelive中的记录相同，例如：

live
sss
ssa
ddd
asa
(dance2)
asaaa
ssa
(bluek2)
jjj
vv
(comp2)
(sad2)
(dance7)

Answer 1

你甚至需要加入friendship表吗？

SELECT p.message
    FROM messageslive p
    WHERE p.username = '{$username1}'
    ORDER BY p.id DESC
    LIMIT 16

如果你只是想建立友谊的存在，也许：

SELECT p.message
    FROM messageslive p
    WHERE p.username = '{$username1}'
        AND EXISTS(SELECT 1
                       FROM friendship f
                       WHERE f.username = p.username
                           OR f.frenusername = p.username)
    ORDER BY p.id DESC
    LIMIT 16

Answer 2

将您的查询更改为此，它应该有效。

$query41 = "SELECT  p.message FROM friendship f
JOIN messageslive p
ON p.username = f.frenusername OR p.username = f.username
WHERE f.frenusername = '{$username1}'
ORDER BY
p.id DESC
LIMIT 0, 16";