更新 这是CASE语句使用的两个表的ddl
CREATE TABLE product_option (
merchant_id smallint unsigned NOT NULL,
product_option_id smallint unsigned NOT NULL AUTO_INCREMENT,
product_option_name varchar(255) NOT NULL DEFAULT '',
product_id int unsigned NOT NULL DEFAULT 0, /* Option may be associated with a product */
package_id int unsigned NOT NULL DEFAULT 0, /* or all products with this package */
PRIMARY KEY pk_product_option (merchant_id,product_option_id),
) TYPE=MyISAM PACK_KEYS=1 COMMENT='Options';
CREATE TABLE package_2_product (
merchant_id smallint unsigned NOT NULL,
package_id int unsigned NOT NULL,
product_id int unsigned NOT NULL,
PRIMARY KEY pk_package_2_product (merchant_id,package_id,product_id)
) TYPE=MyISAM PACK_KEYS=1 COMMENT='Link product to package';
我有一个查询...
SELECT SQL_CALC_FOUND_ROWS
p.*,
CASE p.in_stock_msg WHEN '' THEN 'In stock' ELSE p.in_stock_msg END AS in_stock_msg,
CASE p.out_stock_msg WHEN '' THEN '' ELSE p.out_stock_msg END AS out_stock_msg,
CASE WHEN EXISTS (
SELECT product_option_id
FROM product_option
WHERE merchant_id = 116 AND product_id = p.product_id
UNION
SELECT product_id FROM package_2_product
WHERE merchant_id = 116 AND product_id = p.product_id
) THEN 1 ELSE 0 END AS options_exist,
i.thumbnail,i.thumbnail_width,i.thumbnail_height,
i.title AS thumbnail_title, i.alt AS thumbnail_alt
FROM
product p
INNER JOIN category_2_product c2p ON p.merchant_id=c2p.merchant_id
AND p.product_id=c2p.product_id
AND c2p.category_id = 84
LEFT JOIN product_image i ON p.merchant_id = i.merchant_id
AND p.product_id = i.product_id
AND i.is_default = 1
WHERE
p.merchant_id = 116
AND FIND_IN_SET('live',p.param) > 0
AND FIND_IN_SET('wholesale-only',p.param) = 0
ORDER BY
p.rank, p.product_name
LIMIT 0, 50;
相关部分是案例，当时存在...... 导致查询需要多秒才能运行。如果没有子选择，它将在十分之一秒内完成。
我想知道是否有办法移动这种类型的情况，子选择内部连接以获取相同的数据，而不是为返回的每一行运行子选择。
通过调整Coalesce线和LEFT JOIN（SELECT ...）来尝试下面的查询p1
我收到了这个错误......
错误代码：1054 'on clause'
中的未知列'p1.product_id'这是查询...
SELECT SQL_CALC_FOUND_ROWS
p.*,
CASE p.in_stock_msg WHEN '' THEN 'In stock' ELSE p.in_stock_msg END AS in_stock_msg,
CASE p.out_stock_msg WHEN '' THEN '' ELSE p.out_stock_msg END AS out_stock_msg,
COALESCE(p1.product_option_id, p2.product_id) IS NOT NULL AS options_exist,
i.thumbnail,i.thumbnail_width,i.thumbnail_height,
i.title AS thumbnail_title, i.alt AS thumbnail_alt
FROM
product p
INNER JOIN category_2_product c2p ON p.merchant_id=c2p.merchant_id
AND p.product_id=c2p.product_id
AND c2p.category_id = 84
LEFT JOIN product_image i ON p.merchant_id = i.merchant_id
AND p.product_id = i.product_id
AND i.is_default = 1
LEFT JOIN (
SELECT product_option_id
FROM product_option
WHERE merchant_id = 116
GROUP BY product_id) p1 on p1.product_id = p.product_id
LEFT JOIN (
SELECT product_id
FROM package_2_product
WHERE merchant_id = 116
GROUP BY product_id) p2 on p1.product_id is null and p2.product_id = p.product_id
WHERE
p.merchant_id = 116
AND FIND_IN_SET('live',p.param) > 0
AND FIND_IN_SET('wholesale-only',p.param) = 0
ORDER BY
p.rank, p.product_name
答案 0 :(得分：2)
SELECT SQL_CALC_FOUND_ROWS
p.*,
CASE p.in_stock_msg WHEN '' THEN 'In stock' ELSE p.in_stock_msg END AS in_stock_msg,
CASE p.out_stock_msg WHEN '' THEN '' ELSE p.out_stock_msg END AS out_stock_msg,
COALESCE(p1.product_id, p2.product_id) IS NOT NULL AS options_exist,
i.thumbnail,i.thumbnail_width,i.thumbnail_height,
i.title AS thumbnail_title, i.alt AS thumbnail_alt
FROM
product p
INNER JOIN category_2_product c2p ON p.merchant_id=c2p.merchant_id
AND p.product_id=c2p.product_id
AND c2p.category_id = 84
LEFT JOIN product_image i ON p.merchant_id = i.merchant_id
AND p.product_id = i.product_id
AND i.is_default = 1
LEFT JOIN (
SELECT product_id
FROM product_option
WHERE merchant_id = 116
GROUP BY product_id) p1 on p1.product_id = p.product_id
LEFT JOIN (
SELECT product_id
FROM package_2_product
WHERE merchant_id = 116
GROUP BY product_id) p2 on p1.product_id is null and p2.product_id = p.product_id
WHERE
p.merchant_id = 116
AND FIND_IN_SET('live',p.param) > 0
AND FIND_IN_SET('wholesale-only',p.param) = 0
ORDER BY
p.rank, p.product_name
注意：
on p1.product_id is null被添加到第二个左连接中，以防止在p1已经有结果时执行它。<小时/> 此DDL将创建一个包含足够字段的表，以显示查询正常运行。
create table product_option(merchant_id int, product_id int);
create table package_2_product(merchant_id int, product_id int);
create table category_2_product(merchant_id int, product_id int, category_id int);
create table product_image(merchant_id int, product_id int, is_default int,
thumbnail int, thumbnail_width int, thumbnail_height int, title int, alt int);
create table product(merchant_id int, product_id int, in_stock_msg int,
out_stock_msg int, param int, rank int, product_name int);
答案 1 :(得分：0)
试试这个：
SELECT SQL_CALC_FOUND_ROWS p.*,
CASE p.in_stock_msg
WHEN '' THEN 'In stock'
ELSE p.in_stock_msg
END AS in_stock_msg,
CASE p.out_stock_msg
WHEN '' THEN ''
ELSE p.out_stock_msg
END AS out_stock_msg,
CASE
WHEN Isnull(po.product_option_id)
AND Isnull(p2p.product_id) THEN 0
ELSE 1
END AS options_exist,
i.thumbnail,
i.thumbnail_width,
i.thumbnail_height,
i.title AS thumbnail_title,
i.alt AS thumbnail_alt
FROM product p
INNER JOIN category_2_product c2p
ON p.merchant_id = c2p.merchant_id
AND p.product_id = c2p.product_id
AND c2p.category_id = 84
LEFT JOIN product_image i
ON p.merchant_id = i.merchant_id
AND p.product_id = i.product_id
AND i.is_default = 1
LEFT JOIN product_option po
ON po.merchant_id = 116
AND po.product_id = p.product_id
LEFT JOIN package_2_product p2p
ON p2p.merchant_id = 116
AND p2p.product_id = p.product_id
WHERE p.merchant_id = 116
AND Find_in_set('live', p.param) > 0
AND Find_in_set('wholesale-only', p.param) = 0
GROUP BY p.prduct_id
ORDER BY p.rank,
p.product_name
LIMIT 0, 50;
你需要两个表的索引