Question

我正在尝试通过3个表的联合查询获取消息一切都按预期工作，但是当我尝试限制结果时，查询失败并且不返回任何内容

查询

    SELECT 
        P.patient_name, 
        DM.message, 
        DM.secsince, 
        DM.id, 
        DM.pid, 
        DM.did, 
        DM.mode, 
        DM.date, 
        DM.seen 
    FROM tbl_patient P, 
        tbl_doct D, 
        tbl_doct_messages DM 
    WHERE (DM.did = D.id AND DM.pid = P.id) 
        AND (DM.mode = 'in') 
        AND (D.id = '$id') 
    ORDER BY DM.secsince DESC;

此查询工作正常，并给了我预期的结果

但是当我使用LIMIT时，它会失败，并且由于某种原因不返回任何内容

查询

SELECT 
    P.patient_name, 
    DM.message, 
    DM.secsince, 
    DM.id, 
    DM.pid, 
    DM.did, 
    DM.mode, 
    DM.date, 
    DM.seen 
FROM tbl_patient P, 
    tbl_doct D, 
    tbl_doct_messages DM 
WHERE (DM.did = D.id AND DM.pid = P.id) 
    AND (DM.mode = 'in') 
    AND (D.id = '$id') 
ORDER BY 
   DM.secsince DESC; 
LIMIT=1;

这是完整的php代码

<?php
include("conn.php");
if(mysqli_connect_error($con)) {
    echo "Failed To Connect";
}

$id = $_GET['id'];
$qry = "SELECT P.patient_name, DM.message, DM.secsince, DM.id, DM.pid, DM.did, DM.mode, DM.date, DM.seen 
        FROM tbl_patient P, tbl_doct D, tbl_doct_messages DM 
        WHERE (DM.did = D.id AND DM.pid = P.id) AND (DM.mode = 'in') AND (D.id = '$id') 
        ORDER BY DM.secsince DESC 
        LIMIT=1;";
$res = mysqli_query($con, $qry);
$flag = array();
while(($row = mysqli_fetch_array($res))){
    array_push($flag, $row);
}
echo json_encode($flag); 
mysqli_close($con);     
?>

正如您在这张照片中看到的，它为我提供了没有限制的结果

但是没有结果，所以当我添加 limit

时，mysqli_fetch_array失败

为什么会这样？我基本上没有主意。

Answer 1

因为正确的语法是LIMIT 1而不是LIMIT = 1

Answer 2

更新您的查询

来自

SELECT 
    P.patient_name, 
    DM.message, 
    DM.secsince, 
    DM.id, DM.pid, 
    DM.did, DM.mode, 
    DM.date, DM.seen 
FROM 
    tbl_patient P, 
    tbl_doct D, 
    tbl_doct_messages DM 
WHERE 
    (DM.did = D.id AND DM.pid = P.id) AND 
    (DM.mode = 'in') AND (D.id = '$id') 
ORDER BY 
   DM.secsince DESC 
LIMIT=1

删除 =

SELECT 
    P.patient_name, 
    DM.message, 
    DM.secsince, 
    DM.id, DM.pid, 
    DM.did, DM.mode, 
    DM.date, DM.seen 
FROM 
    tbl_patient P, 
    tbl_doct D, 
    tbl_doct_messages DM 
WHERE 
    (DM.did = D.id AND DM.pid = P.id) AND 
    (DM.mode = 'in') AND (D.id = '$id') 
ORDER BY 
   DM.secsince DESC 
LIMIT 1

PHP Mysql LIMIT查询失败

2 个答案: