ฉันเข้าใจอย่างถ่องแท้ว่าทำไมถึงมีความจำเป็น - อย่างน้อยสำหรับฉันมันมีประโยชน์ในระหว่างการสร้างต้นแบบอย่างรวดเร็วเมื่อมีตารางจำนวนมากที่จำเป็นต้องเข้าร่วมรวมถึงการรวมภายในหลายอย่าง ทันทีที่ชื่อคอลัมน์เหมือนกันใน wild wildcard ฟิลด์ "jointable. *" ที่สองค่าของฟิลด์หลักของตารางจะถูกแทนที่ด้วยค่า jointable เกิดข้อผิดพลาดทำให้หงุดหงิดและละเมิด DRY เมื่อต้องระบุฟิลด์ตารางด้วยตนเองด้วยชื่อแทนซ้ำแล้วซ้ำอีก ...
นี่คือฟังก์ชั่น PHP (Wordpress) เพื่อให้ได้สิ่งนี้ผ่านการสร้างรหัสพร้อมกับตัวอย่างของวิธีการใช้งาน ในตัวอย่างจะใช้เพื่อสร้างคิวรีแบบกำหนดเองที่จะให้ฟิลด์ของโพสต์ WordPress ที่เกี่ยวข้องที่ถูกอ้างอิงผ่านฟิลด์ฟิลด์กำหนดเองขั้นสูงอย่างรวดเร็ว
function prefixed_table_fields_wildcard($table, $alias)
{
global $wpdb;
$columns = $wpdb->get_results("SHOW COLUMNS FROM $table", ARRAY_A);
$field_names = array();
foreach ($columns as $column)
{
$field_names[] = $column["Field"];
}
$prefixed = array();
foreach ($field_names as $field_name)
{
$prefixed[] = "`{$alias}`.`{$field_name}` AS `{$alias}.{$field_name}`";
}
return implode(", ", $prefixed);
}
function test_prefixed_table_fields_wildcard()
{
global $wpdb;
$query = "
SELECT
" . prefixed_table_fields_wildcard($wpdb->posts, 'campaigns') . ",
" . prefixed_table_fields_wildcard($wpdb->posts, 'venues') . "
FROM $wpdb->posts AS campaigns
LEFT JOIN $wpdb->postmeta meta1 ON (meta1.meta_key = 'venue' AND campaigns.ID = meta1.post_id)
LEFT JOIN $wpdb->posts venues ON (venues.post_status = 'publish' AND venues.post_type = 'venue' AND venues.ID = meta1.meta_value)
WHERE 1
AND campaigns.post_status = 'publish'
AND campaigns.post_type = 'campaign'
LIMIT 1
";
echo "<pre>$query</pre>";
$posts = $wpdb->get_results($query, OBJECT);
echo "<pre>";
print_r($posts);
echo "</pre>";
}
ผลลัพธ์:
SELECT
`campaigns`.`ID` AS `campaigns.ID`, `campaigns`.`post_author` AS `campaigns.post_author`, `campaigns`.`post_date` AS `campaigns.post_date`, `campaigns`.`post_date_gmt` AS `campaigns.post_date_gmt`, `campaigns`.`post_content` AS `campaigns.post_content`, `campaigns`.`post_title` AS `campaigns.post_title`, `campaigns`.`post_excerpt` AS `campaigns.post_excerpt`, `campaigns`.`post_status` AS `campaigns.post_status`, `campaigns`.`comment_status` AS `campaigns.comment_status`, `campaigns`.`ping_status` AS `campaigns.ping_status`, `campaigns`.`post_password` AS `campaigns.post_password`, `campaigns`.`post_name` AS `campaigns.post_name`, `campaigns`.`to_ping` AS `campaigns.to_ping`, `campaigns`.`pinged` AS `campaigns.pinged`, `campaigns`.`post_modified` AS `campaigns.post_modified`, `campaigns`.`post_modified_gmt` AS `campaigns.post_modified_gmt`, `campaigns`.`post_content_filtered` AS `campaigns.post_content_filtered`, `campaigns`.`post_parent` AS `campaigns.post_parent`, `campaigns`.`guid` AS `campaigns.guid`, `campaigns`.`menu_order` AS `campaigns.menu_order`, `campaigns`.`post_type` AS `campaigns.post_type`, `campaigns`.`post_mime_type` AS `campaigns.post_mime_type`, `campaigns`.`comment_count` AS `campaigns.comment_count`,
`venues`.`ID` AS `venues.ID`, `venues`.`post_author` AS `venues.post_author`, `venues`.`post_date` AS `venues.post_date`, `venues`.`post_date_gmt` AS `venues.post_date_gmt`, `venues`.`post_content` AS `venues.post_content`, `venues`.`post_title` AS `venues.post_title`, `venues`.`post_excerpt` AS `venues.post_excerpt`, `venues`.`post_status` AS `venues.post_status`, `venues`.`comment_status` AS `venues.comment_status`, `venues`.`ping_status` AS `venues.ping_status`, `venues`.`post_password` AS `venues.post_password`, `venues`.`post_name` AS `venues.post_name`, `venues`.`to_ping` AS `venues.to_ping`, `venues`.`pinged` AS `venues.pinged`, `venues`.`post_modified` AS `venues.post_modified`, `venues`.`post_modified_gmt` AS `venues.post_modified_gmt`, `venues`.`post_content_filtered` AS `venues.post_content_filtered`, `venues`.`post_parent` AS `venues.post_parent`, `venues`.`guid` AS `venues.guid`, `venues`.`menu_order` AS `venues.menu_order`, `venues`.`post_type` AS `venues.post_type`, `venues`.`post_mime_type` AS `venues.post_mime_type`, `venues`.`comment_count` AS `venues.comment_count`
FROM wp_posts AS campaigns
LEFT JOIN wp_postmeta meta1 ON (meta1.meta_key = 'venue' AND campaigns.ID = meta1.post_id)
LEFT JOIN wp_posts venues ON (venues.post_status = 'publish' AND venues.post_type = 'venue' AND venues.ID = meta1.meta_value)
WHERE 1
AND campaigns.post_status = 'publish'
AND campaigns.post_type = 'campaign'
LIMIT 1
Array
(
[0] => stdClass Object
(
[campaigns.ID] => 33
[campaigns.post_author] => 2
[campaigns.post_date] => 2012-01-16 19:19:10
[campaigns.post_date_gmt] => 2012-01-16 19:19:10
[campaigns.post_content] => Lorem ipsum
[campaigns.post_title] => Lorem ipsum
[campaigns.post_excerpt] =>
[campaigns.post_status] => publish
[campaigns.comment_status] => closed
[campaigns.ping_status] => closed
[campaigns.post_password] =>
[campaigns.post_name] => lorem-ipsum
[campaigns.to_ping] =>
[campaigns.pinged] =>
[campaigns.post_modified] => 2012-01-16 21:01:55
[campaigns.post_modified_gmt] => 2012-01-16 21:01:55
[campaigns.post_content_filtered] =>
[campaigns.post_parent] => 0
[campaigns.guid] => http://example.com/?p=33
[campaigns.menu_order] => 0
[campaigns.post_type] => campaign
[campaigns.post_mime_type] =>
[campaigns.comment_count] => 0
[venues.ID] => 84
[venues.post_author] => 2
[venues.post_date] => 2012-01-16 20:12:05
[venues.post_date_gmt] => 2012-01-16 20:12:05
[venues.post_content] => Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
[venues.post_title] => Lorem ipsum venue
[venues.post_excerpt] =>
[venues.post_status] => publish
[venues.comment_status] => closed
[venues.ping_status] => closed
[venues.post_password] =>
[venues.post_name] => lorem-ipsum-venue
[venues.to_ping] =>
[venues.pinged] =>
[venues.post_modified] => 2012-01-16 20:53:37
[venues.post_modified_gmt] => 2012-01-16 20:53:37
[venues.post_content_filtered] =>
[venues.post_parent] => 0
[venues.guid] => http://example.com/?p=84
[venues.menu_order] => 0
[venues.post_type] => venue
[venues.post_mime_type] =>
[venues.comment_count] => 0
)
)