如何在 MySQL 中使用准备好的语句创建动态列？
How to create dynamic columns using prepared statements in MySQL?
我有 4 个相互关联的表。
CREATE TABLE `location` (
`id` bigint(20) UNSIGNED NOT NULL AUTO_INCREMENT,
`name` varchar(255) COLLATE utf8mb4_unicode_ci NOT NULL,
PRIMARY KEY (id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
INSERT INTO `location` (`id`, `name`) VALUES
(1, 'Dallas'),
(2, 'Boston'),
(3, 'Houston');
CREATE TABLE `item` (
`id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`brand` varchar(255) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
PRIMARY KEY (id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
INSERT INTO `item` (`id`, `brand`) VALUES
(1, 'Nissan Almera M/T 2009-2015'),
(2, 'Toyota Corolla A/T 2005-2012'),
(3, 'Nissan Terra A/T 2010-2017'),
(4, 'Suzuki Esteem M/T 1980-1990'),
(5, 'Toyota Fortuner A/T 2014-2020');
CREATE TABLE `item_in` (
`id` bigint(20) UNSIGNED NOT NULL AUTO_INCREMENT,
`location_id` bigint(20) UNSIGNED NOT NULL,
`item_id` bigint(20) UNSIGNED NOT NULL,
`quantity` int(11) DEFAULT NULL,
PRIMARY KEY (id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
INSERT INTO `item_in` (`id`, `location_id`, `item_id`, `quantity`) VALUES
(1, 1, 1, 1000),
(2, 1, 2, 500),
(3, 2, 2, 200),
(4, 2, 2, 300),
(5, 3, 3, 300),
(6, 1, 3, 800),
(7, 3, 5, 300),
(8, 3, 4, 400);
CREATE TABLE `item_out` (
`id` bigint(20) UNSIGNED NOT NULL AUTO_INCREMENT,
`location_id` bigint(20) UNSIGNED NOT NULL,
`item_id` bigint(20) UNSIGNED NOT NULL,
`quantity` int(11) DEFAULT NULL,
PRIMARY KEY (id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
INSERT INTO `item_out` (`id`, `location_id`, `item_id`, `quantity`) VALUES
(1, 1, 2, 20),
(2, 1, 1, 25),
(3, 2, 2, 25),
(4, 3, 3, 25),
(5, 3, 5, 10),
(6, 3, 4, 15),
(7, 1, 1, 200),
(8, 2, 2, 50);
使用动态 SQL，我能够根据它们的位置和项目获得每个项目的单独剩余数量（item_in 数量减去 item_out 数量）并获得位置名称作为列。 （见下面的代码）：
SET @sql = NULL, @sql1 = NULL, @sql2 = NULL;
SELECT GROUP_CONCAT( DISTINCT
CONCAT('SUM(CASE WHEN `location_id` = ''',`location_id`, ''' THEN quantity END) AS ',`name`))
INTO @sql1
FROM item_in
JOIN location on location.id = item_in.location_id;
SELECT GROUP_CONCAT( DISTINCT
CONCAT('SUM(CASE WHEN `location_id` = ''',`location_id`, ''' THEN quantity END) AS ',`name`))
INTO @sql2
FROM item_out
JOIN location on location.id = item_out.location_id;
SET @sql = CONCAT('SELECT item.brand AS Item, IFNULL(item_in.Dallas, 0) - IFNULL(item_out.Dallas, 0) AS Dallas, IFNULL(item_in.Boston, 0) - IFNULL(item_out.Boston, 0) AS Boston, IFNULL(item_in.Houston, 0) - IFNULL(item_out.Houston, 0) AS Houston FROM item LEFT JOIN (SELECT item_in.item_id, ', @sql1, ' FROM item_in
GROUP BY item_in.item_id) AS item_in ON item.id = item_in.item_id LEFT JOIN (SELECT item_out.item_id, ', @sql2, ' FROM item_out
GROUP BY item_out.item_id) AS item_out ON item.id = item_out.item_id');
PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
结果:
Item | Dallas | Boston | Houston
Nissan Almera M/T 2009-2015 775 0 0
Toyota Corolla A/T 2005-2012 480 425 0
Nissan Terra A/T 2010-2017 800 0 275
Suzuki Esteem M/T 1980-1990 0 0 385
Toyota Fortuner A/T 2014-2020 0 0 290
我的问题是，由于用户可以随时添加新位置，我该如何更改代码以便动态显示位置名称列而不是在查询中手动对它们进行硬编码？如果有人可以看一下我的代码，我将非常感谢您的帮助。我遇到的唯一问题是如何不对这些行进行硬编码并动态地执行它们：
IFNULL(item_in.Dallas, 0) - IFNULL(item_out.Dallas, 0) AS Dallas, IFNULL(item_in.Boston, 0) - IFNULL(item_out.Boston, 0) AS Boston, IFNULL(item_in.Houston, 0) - IFNULL(item_out.Houston, 0) AS Houston
例如，考虑以下使用 PHP 和 mysqli_ API。 （我用过程序代码，但dbo会更有效率）...
<?php
/*
DROP TABLE IF EXISTS location;
CREATE TABLE `location` (
`id` bigint(20) UNSIGNED NOT NULL AUTO_INCREMENT,
`name` varchar(255) NOT NULL,
PRIMARY KEY (id)
);
INSERT INTO `location` (`id`, `name`) VALUES
(1, 'Dallas'),
(2, 'Boston'),
(3, 'Houston');
DROP TABLE IF EXISTS item;
CREATE TABLE `item` (
`id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`brand` varchar(255) DEFAULT NULL,
PRIMARY KEY (id)
);
INSERT INTO `item` (`id`, `brand`) VALUES
(1, 'Nissan Almera M/T 2009-2015'),
(2, 'Toyota Corolla A/T 2005-2012'),
(3, 'Nissan Terra A/T 2010-2017'),
(4, 'Suzuki Esteem M/T 1980-1990'),
(5, 'Toyota Fortuner A/T 2014-2020');
DROP TABLE IF EXISTS item_in;
CREATE TABLE `item_in` (
`id` bigint(20) UNSIGNED NOT NULL AUTO_INCREMENT,
`location_id` bigint(20) UNSIGNED NOT NULL,
`item_id` bigint(20) UNSIGNED NOT NULL,
`quantity` int(11) DEFAULT NULL,
PRIMARY KEY (id)
);
INSERT INTO `item_in` (`id`, `location_id`, `item_id`, `quantity`) VALUES
(1, 1, 1, 1000),
(2, 1, 2, 500),
(3, 2, 2, 200),
(4, 2, 2, 300),
(5, 3, 3, 300),
(6, 1, 3, 800),
(7, 3, 5, 300),
(8, 3, 4, 400);
DROP TABLE IF EXISTS item_out;
CREATE TABLE `item_out` (
`id` bigint(20) UNSIGNED NOT NULL AUTO_INCREMENT,
`location_id` bigint(20) UNSIGNED NOT NULL,
`item_id` bigint(20) UNSIGNED NOT NULL,
`quantity` int(11) DEFAULT NULL,
PRIMARY KEY (id)
);
INSERT INTO `item_out` (`id`, `location_id`, `item_id`, `quantity`) VALUES
(1, 1, 2, 20),
(2, 1, 1, 25),
(3, 2, 2, 25),
(4, 3, 3, 25),
(5, 3, 5, 10),
(6, 3, 4, 15),
(7, 1, 1, 200),
(8, 2, 2, 50);
*/
require('path/to/connect.ion');
$query = "
SELECT l.name city
, i.brand item
, SUM(x.quantity) total
FROM
( SELECT location_id,item_id,'in' type, quantity FROM item_in
UNION ALL
SELECT location_id,item_id,'out',quantity*-1 FROM item_out
) x
JOIN location l
ON l.id = x.location_id
JOIN item i
ON i.id = x.item_id
GROUP
BY item
, city
ORDER
BY city
, item
";
$result = mysqli_query($db,$query);
$array = array();
while($row = mysqli_fetch_assoc($result)){
$array[] = $row;
}
foreach($array as $v){
$new_array[$v['city']][$v['item']] = $v['total'];
}
print_r($new_array);
?>
输出：
Array
(
[Boston] => Array
(
[Toyota Corolla A/T 2005-2012] => 425
)
[Dallas] => Array
(
[Nissan Almera M/T 2009-2015] => 775
[Nissan Terra A/T 2010-2017] => 800
[Toyota Corolla A/T 2005-2012] => 480
)
[Houston] => Array
(
[Nissan Terra A/T 2010-2017] => 275
[Suzuki Esteem M/T 1980-1990] => 385
[Toyota Fortuner A/T 2014-2020] => 290
)
)
或者您可以在 $new_array[$v['city']][$v['item']] = $v['total']; 中交换城市和物品，以获得：
Array
(
[Toyota Corolla A/T 2005-2012] => Array
(
[Boston] => 425
[Dallas] => 480
)
[Nissan Almera M/T 2009-2015] => Array
(
[Dallas] => 775
)
[Nissan Terra A/T 2010-2017] => Array
(
[Dallas] => 800
[Houston] => 275
)
[Suzuki Esteem M/T 1980-1990] => Array
(
[Houston] => 385
)
[Toyota Fortuner A/T 2014-2020] => Array
(
[Houston] => 290
)
)
我有 4 个相互关联的表。
CREATE TABLE `location` (
`id` bigint(20) UNSIGNED NOT NULL AUTO_INCREMENT,
`name` varchar(255) COLLATE utf8mb4_unicode_ci NOT NULL,
PRIMARY KEY (id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
INSERT INTO `location` (`id`, `name`) VALUES
(1, 'Dallas'),
(2, 'Boston'),
(3, 'Houston');
CREATE TABLE `item` (
`id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`brand` varchar(255) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
PRIMARY KEY (id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
INSERT INTO `item` (`id`, `brand`) VALUES
(1, 'Nissan Almera M/T 2009-2015'),
(2, 'Toyota Corolla A/T 2005-2012'),
(3, 'Nissan Terra A/T 2010-2017'),
(4, 'Suzuki Esteem M/T 1980-1990'),
(5, 'Toyota Fortuner A/T 2014-2020');
CREATE TABLE `item_in` (
`id` bigint(20) UNSIGNED NOT NULL AUTO_INCREMENT,
`location_id` bigint(20) UNSIGNED NOT NULL,
`item_id` bigint(20) UNSIGNED NOT NULL,
`quantity` int(11) DEFAULT NULL,
PRIMARY KEY (id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
INSERT INTO `item_in` (`id`, `location_id`, `item_id`, `quantity`) VALUES
(1, 1, 1, 1000),
(2, 1, 2, 500),
(3, 2, 2, 200),
(4, 2, 2, 300),
(5, 3, 3, 300),
(6, 1, 3, 800),
(7, 3, 5, 300),
(8, 3, 4, 400);
CREATE TABLE `item_out` (
`id` bigint(20) UNSIGNED NOT NULL AUTO_INCREMENT,
`location_id` bigint(20) UNSIGNED NOT NULL,
`item_id` bigint(20) UNSIGNED NOT NULL,
`quantity` int(11) DEFAULT NULL,
PRIMARY KEY (id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
INSERT INTO `item_out` (`id`, `location_id`, `item_id`, `quantity`) VALUES
(1, 1, 2, 20),
(2, 1, 1, 25),
(3, 2, 2, 25),
(4, 3, 3, 25),
(5, 3, 5, 10),
(6, 3, 4, 15),
(7, 1, 1, 200),
(8, 2, 2, 50);
使用动态 SQL，我能够根据它们的位置和项目获得每个项目的单独剩余数量（item_in 数量减去 item_out 数量）并获得位置名称作为列。 （见下面的代码）：
SET @sql = NULL, @sql1 = NULL, @sql2 = NULL;
SELECT GROUP_CONCAT( DISTINCT
CONCAT('SUM(CASE WHEN `location_id` = ''',`location_id`, ''' THEN quantity END) AS ',`name`))
INTO @sql1
FROM item_in
JOIN location on location.id = item_in.location_id;
SELECT GROUP_CONCAT( DISTINCT
CONCAT('SUM(CASE WHEN `location_id` = ''',`location_id`, ''' THEN quantity END) AS ',`name`))
INTO @sql2
FROM item_out
JOIN location on location.id = item_out.location_id;
SET @sql = CONCAT('SELECT item.brand AS Item, IFNULL(item_in.Dallas, 0) - IFNULL(item_out.Dallas, 0) AS Dallas, IFNULL(item_in.Boston, 0) - IFNULL(item_out.Boston, 0) AS Boston, IFNULL(item_in.Houston, 0) - IFNULL(item_out.Houston, 0) AS Houston FROM item LEFT JOIN (SELECT item_in.item_id, ', @sql1, ' FROM item_in
GROUP BY item_in.item_id) AS item_in ON item.id = item_in.item_id LEFT JOIN (SELECT item_out.item_id, ', @sql2, ' FROM item_out
GROUP BY item_out.item_id) AS item_out ON item.id = item_out.item_id');
PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
结果:
Item | Dallas | Boston | Houston
Nissan Almera M/T 2009-2015 775 0 0
Toyota Corolla A/T 2005-2012 480 425 0
Nissan Terra A/T 2010-2017 800 0 275
Suzuki Esteem M/T 1980-1990 0 0 385
Toyota Fortuner A/T 2014-2020 0 0 290
我的问题是，由于用户可以随时添加新位置，我该如何更改代码以便动态显示位置名称列而不是在查询中手动对它们进行硬编码？如果有人可以看一下我的代码，我将非常感谢您的帮助。我遇到的唯一问题是如何不对这些行进行硬编码并动态地执行它们：
IFNULL(item_in.Dallas, 0) - IFNULL(item_out.Dallas, 0) AS Dallas, IFNULL(item_in.Boston, 0) - IFNULL(item_out.Boston, 0) AS Boston, IFNULL(item_in.Houston, 0) - IFNULL(item_out.Houston, 0) AS Houston
例如，考虑以下使用 PHP 和 mysqli_ API。 （我用过程序代码，但dbo会更有效率）...
<?php
/*
DROP TABLE IF EXISTS location;
CREATE TABLE `location` (
`id` bigint(20) UNSIGNED NOT NULL AUTO_INCREMENT,
`name` varchar(255) NOT NULL,
PRIMARY KEY (id)
);
INSERT INTO `location` (`id`, `name`) VALUES
(1, 'Dallas'),
(2, 'Boston'),
(3, 'Houston');
DROP TABLE IF EXISTS item;
CREATE TABLE `item` (
`id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`brand` varchar(255) DEFAULT NULL,
PRIMARY KEY (id)
);
INSERT INTO `item` (`id`, `brand`) VALUES
(1, 'Nissan Almera M/T 2009-2015'),
(2, 'Toyota Corolla A/T 2005-2012'),
(3, 'Nissan Terra A/T 2010-2017'),
(4, 'Suzuki Esteem M/T 1980-1990'),
(5, 'Toyota Fortuner A/T 2014-2020');
DROP TABLE IF EXISTS item_in;
CREATE TABLE `item_in` (
`id` bigint(20) UNSIGNED NOT NULL AUTO_INCREMENT,
`location_id` bigint(20) UNSIGNED NOT NULL,
`item_id` bigint(20) UNSIGNED NOT NULL,
`quantity` int(11) DEFAULT NULL,
PRIMARY KEY (id)
);
INSERT INTO `item_in` (`id`, `location_id`, `item_id`, `quantity`) VALUES
(1, 1, 1, 1000),
(2, 1, 2, 500),
(3, 2, 2, 200),
(4, 2, 2, 300),
(5, 3, 3, 300),
(6, 1, 3, 800),
(7, 3, 5, 300),
(8, 3, 4, 400);
DROP TABLE IF EXISTS item_out;
CREATE TABLE `item_out` (
`id` bigint(20) UNSIGNED NOT NULL AUTO_INCREMENT,
`location_id` bigint(20) UNSIGNED NOT NULL,
`item_id` bigint(20) UNSIGNED NOT NULL,
`quantity` int(11) DEFAULT NULL,
PRIMARY KEY (id)
);
INSERT INTO `item_out` (`id`, `location_id`, `item_id`, `quantity`) VALUES
(1, 1, 2, 20),
(2, 1, 1, 25),
(3, 2, 2, 25),
(4, 3, 3, 25),
(5, 3, 5, 10),
(6, 3, 4, 15),
(7, 1, 1, 200),
(8, 2, 2, 50);
*/
require('path/to/connect.ion');
$query = "
SELECT l.name city
, i.brand item
, SUM(x.quantity) total
FROM
( SELECT location_id,item_id,'in' type, quantity FROM item_in
UNION ALL
SELECT location_id,item_id,'out',quantity*-1 FROM item_out
) x
JOIN location l
ON l.id = x.location_id
JOIN item i
ON i.id = x.item_id
GROUP
BY item
, city
ORDER
BY city
, item
";
$result = mysqli_query($db,$query);
$array = array();
while($row = mysqli_fetch_assoc($result)){
$array[] = $row;
}
foreach($array as $v){
$new_array[$v['city']][$v['item']] = $v['total'];
}
print_r($new_array);
?>
输出：
Array
(
[Boston] => Array
(
[Toyota Corolla A/T 2005-2012] => 425
)
[Dallas] => Array
(
[Nissan Almera M/T 2009-2015] => 775
[Nissan Terra A/T 2010-2017] => 800
[Toyota Corolla A/T 2005-2012] => 480
)
[Houston] => Array
(
[Nissan Terra A/T 2010-2017] => 275
[Suzuki Esteem M/T 1980-1990] => 385
[Toyota Fortuner A/T 2014-2020] => 290
)
)
或者您可以在 $new_array[$v['city']][$v['item']] = $v['total']; 中交换城市和物品，以获得：
Array
(
[Toyota Corolla A/T 2005-2012] => Array
(
[Boston] => 425
[Dallas] => 480
)
[Nissan Almera M/T 2009-2015] => Array
(
[Dallas] => 775
)
[Nissan Terra A/T 2010-2017] => Array
(
[Dallas] => 800
[Houston] => 275
)
[Suzuki Esteem M/T 1980-1990] => Array
(
[Houston] => 385
)
[Toyota Fortuner A/T 2014-2020] => Array
(
[Houston] => 290
)
)