Question

正如标题所示，我想基于另一个表中的列的值对一个表执行INSERT查询，以尝试创建等待列表类型系统。这是我的代码：

$sql = "INSERT INTO bookings (username, tourDate, tourTime, tourNumber, guests) 
VALUES ('$username', '$tour_date', '$tour_time', '$tour_num', '$guests')";

$qry = "UPDATE tours
SET available = available-(1+$guests)
WHERE tourNum = '$tour_num'";

"INSERT INTO waitingList (username, tourDate, tourTime, tourNumber, guests) 
VALUES ('$username', '$tour_date', '$tour_time', '$tour_num', '$guests')";

我想要的是：

IF
available column in tours does not = 0
THEN
$sql
ELSE 
insert into waitingList

'waitingList'是一个表格，其中包含与“预订”相同的字段

到目前为止，每次尝试都未能取得这些成果。

我该怎么做？

Answer 1

要在表格上选择值并将其插入另一个表格，您可以使用此

INSERT INTO table1 (column_name1, column_name2)
SELECT column_name1, column_name2 FROM table2
WHERE column_name1 = "x";

Answer 2

假设您正在使用PDO扩展，您应该尝试这样的事情：

<?php
$db = new PDO('mysql:Host=localhost;dbname=testdb;charset=utf8' , 'yourUserName', 'pw');
$stmt = $db->query("SELECT * FROM tours");
$rowCount = $stmt->rowCount();
if ($rowCount > 0) {
    $stmt = "INSERT INTO bookings 
    (username, tourDate, tourTime, tourNumber, guests) 
    VALUES ('$username', '$tour_date', '$tour_time', '$tour_num', '$guests')";
    $updateStmt = "UPDATE tours
    SET available = available-(1+$guests)
    WHERE tourNum = '$tour_num'";
    $query = $db->exec($stmt);
    $updateQuery = $db->exec($updateStmt);
}
else {
    $stmt = "INSERT INTO waitingList 
    (username, tourDate, tourTime, tourNumber, guests) 
    VALUES ('$username', '$tour_date', '$tour_time', '$tour_num', '$guests')";
    $query = $db->exec($stmt);
}

在SELECT查询中使用“*”有时不太好，即使这种方式有效，您也应该尝试使用更具体的字段，如表的主键。

Answer 3

您需要为此使用innoDB表和事务。另外，我可以推荐PDO吗？

伪代码

qty = guests+1;

INSERT INTO bookings
Begin transaction
Select available from tours where tourNum = :tour_number
If selected available - qty <= 0
    update tours set available to 0 where tourNum = :tour_number
    insert into waiting list
else
    update tours set available to available-qty
endif
Commit Transaction

MYSQL根据另一个表

3 个答案: