在此查询,我也想选择一个第三列,wp_postmeta.post_id
,在相同的查询。我无法弄清楚如何做到这一点,而不通过JOIN涉及subquerying其追加。是不是有一个更简单更简单的方法,无需使用子查询的? (愿意于子认输如果解决方案是有效的,不会占用过多资源密集型的。)
MariaDB的10.1
create table wp_posts ( ID integer primary key auto_increment, post_title varchar(30), post_type varchar(30) );
✓
create table wp_postmeta ( ID integer primary key auto_increment, post_id integer, meta_key varchar(30) not null default '_regular_price', meta_value integer not null );
✓
insert into wp_posts (post_title, post_type) values ('Apple Pie','Product'), ('French Toast','Product'), ('Shepards Pie','Product'), ('Jam Pie','Product'), ('Jam Pie','Product'), ('Plate','Not a Product'), ('Bucket','Not a Product'), ('Chequebook','Not a Product'), ('French Toast','Product'), ('French Toast','Product'), ('Banana','Product'), ('Banana','Product'), ('Banana','Product');
✓
insert into wp_postmeta (post_id, meta_value) values (1,10), (2,5), (3,9), (4,8), (5,11), (6,12), (7,10), (8,6), (9,1), (10,1), (11,7), (12,2), (13,2);
✓
SELECT wp_posts.post_title, MIN(wp_postmeta.meta_value) FROM wp_postmeta JOIN wp_posts ON wp_postmeta.post_id = wp_posts.id WHERE wp_posts.post_type = 'Product' AND wp_postmeta.meta_key = '_regular_price' GROUP BY wp_posts.post_title ORDER BY wp_posts.post_title
post_title | MIN(wp_postmeta.meta_value) :----------- | --------------------------: Apple Pie | 10 Banana | 2 French Toast | 1 Jam Pie | 8 Shepards Pie | 9
分贝<>小提琴here
编辑:我并不清楚,在我原来的问题不够明确, - 我要崩溃重复post_titles
并使用对应wp_postmeta.post_id
的MIN(pm.meta_value)
如果我正确地跟着你,你的问题可以利用窗口函数来解决:
SELECT x.post_title, x.id
FROM (
SELECT wp_posts.post_title, wp_postmeta.id, ROW_NUMBER() OVER (PARTITION BY wp_posts.post_title ORDER BY wp_postmeta.meta_value) rn
FROM wp_postmeta
INNER JOIN wp_posts ON wp_postmeta.post_id = wp_posts.id
WHERE wp_posts.post_type = 'Product' AND wp_postmeta.meta_key = '_regular_price'
) x WHERE x.rn = 1;
窗函数去这样的用例(如果我的理解是正确的)的方式。他们通常在效率和可读性方面击败其他解决方案。
如果您的RDBMS不支持窗口功能,一个解决方案是用NOT EXISTS条件,确保有是对于给定的文章标题更小的meta值没有记录使用相关子查询。
SELECT p.post_title, MIN(m.id)
FROM
wp_postmeta m
INNER JOIN wp_posts p
ON p.id = m.post_id
AND p.post_type = 'Product'
WHERE
m.meta_key = '_regular_price'
AND NOT EXISTS (
SELECT 1
FROM
wp_postmeta m1
INNER JOIN wp_posts p1
ON p1.id = m1.post_id
AND p1.post_type = 'Product'
WHERE
m1.meta_key = '_regular_price'
AND p1.post_title = p.post_title
AND m1.meta_value < m.meta_value
)
GROUP BY p.post_title
注:我做了一个小的清洁您的SQL(添加表的别名运来一些条件,然后在相关的条款加入)。
你就不能将其包含在GROUP BY
?
SELECT p.post_title, p.id, MIN(pm.meta_value)
FROM wp_postmeta pm JOIN
wp_posts p
ON pm.post_id = p.id
WHERE p.post_type = 'Product' AND pm.meta_key = '_regular_price'
GROUP BY p.post_title, p.id
ORDER BY p.post_title;
该post_id
是一样的p.id
,所以你不妨利用这一点。
编辑:
如果标题可以重来,然后只需使用一个相关子查询:
SELECT p.post_title, p.id, pm.meta_value
FROM wp_postmeta pm JOIN
wp_posts p
ON pm.post_id = p.id
WHERE p.post_type = 'Product' AND
pm.meta_key = '_regular_price' AND
pm.meta_value = (SELECT MIN(pm2.meta_value)
FROM wp_postmeta pm2 JOIN
wp_posts p2
ON pm2.post_id = p2.id
WHERE p2.post_title = p.post_title
)
ORDER BY p.post_title;
你可以用CTE托盘:
WITH T1
AS ( SELECT post_title, MIN(id) AS ID
FROM wp_posts
GROUP BY post_title )
SELECT T1.ID, wp_posts.post_title, MIN(wp_postmeta.meta_value)
FROM wp_postmeta
JOIN wp_posts ON wp_postmeta.post_id = wp_posts.id
JOIN T1 ON T1.post_title = wp_posts.post_title
WHERE wp_posts.post_type = 'Product'
AND wp_postmeta.meta_key = '_regular_price'
GROUP BY T1.ID, wp_posts.post_title
ORDER BY wp_posts.post_title;
编辑:
你的表wp_posts应该是这样的
Id, post_title, post_type
1, 'Apple Pie','Product'
2, 'French Toast','Product'
3, 'Shepards Pie','Product'
4, 'Jam Pie','Product'
5, 'Plate','Not a Product'
6, 'Bucket','Not a Product'
7, 'Chequebook','Not a Product'
8, 'Banana','Product'
比你有这样的wp_postmeta表数据
post_id, meta_value
1, 10
2, 5
3, 9
4, 8
4, 11
5, 12
6, 10
7, 6
2, 1
2, 1
8, 7
8, 2
8, 2
和查询这个样子
SELECT wp_postmeta.post_id, wp_posts.post_title, MIN(wp_postmeta.meta_value)
FROM wp_postmeta
JOIN wp_posts ON wp_postmeta.post_id = wp_posts.id
WHERE wp_posts.post_type = 'Product'
AND wp_postmeta.meta_key = 'REG PRICE'
GROUP BY wp_postmeta.post_id, wp_posts.post_title
ORDER BY wp_posts.post_title;