似乎无法选择WELL_CMPLTN_ID的最大值

Question

SELECT w.well_id,
w.WELL_NR,
w.WELL_NM,
w.WELL_API_NR,
ws.WELL_SGMNT_SIDE_TRCK_CD,
wc.WELL_CMPLTN_CD,
wc.WELL_SGMNT_ID,
wc.WELL_CMPLTN_ID
FROM WELL W
JOIN WELL_SGMNT ws
ON ws.well_id=w.well_id
JOIN WELL_CMPLTN wc
ON ws.WELL_SGMNT_ID=wc.WELL_SGMNT_ID
WHERE w.well_id    ='13030';

此查询的结果如下，但我想选择WELL_CMPLTN_ID的最大值。

Answer 1

试试这个

<?php

$con = mysqli_connect("localhost", "root", "password", "databasename");

$username = $_POST["username"];

$statement = mysqli_prepare($con, "SELECT * FROM user WHERE username = ?");

mysqli_stmt_bind_param($statement, "s", $username);

mysqli_stmt_execute($statement);

mysqli_stmt_store_result($statement);

mysqli_stmt_bind_result($statement, $user_id, $username);

$response["success"] = false;  

while(mysqli_stmt_fetch($statement)){

$response["success"] = true;  

$response["username"] = $username;

echo json_encode($response);

?>

Answer 2

你可以试试这个：

SELECT * FROM(
    SELECT w.well_id,
    w.WELL_NR,
    w.WELL_NM,
    w.WELL_API_NR,
    ws.WELL_SGMNT_SIDE_TRCK_CD,
    wc.WELL_CMPLTN_CD,
    wc.WELL_SGMNT_ID,
    wc.WELL_CMPLTN_ID
    FROM WELL W
    JOIN WELL_SGMNT ws
    ON ws.well_id=w.well_id
    JOIN WELL_CMPLTN wc
    ON ws.WELL_SGMNT_ID=wc.WELL_SGMNT_ID
    WHERE w.well_id    ='13030
    ORDER BY wc.WELL_CMPLTN_CD DESC
    )
WHERE ROWNUM = 1;

我希望它有所帮助！