这是您日志中的第二个查询，正在查看其他查询。为了帮助解决这个问题，我稍微重组以摆脱子查询并变成 INNER JOIN。此外，为了帮助不了解您的表格的其他人，请始终将您的字段引用限定为 table.column 或 alias.column，例如了解您的 level_depth、nleft、nright 来自哪里。它可能有助于索引。
对于索引，每个表我都会有以下内容。
ps_category, index ON( active, id_category, id_lang, nleft, nright, level_depth )
ps_category_lang, index ON( id_category, id_shop, id_lang )
ps_category_shop, index ON( id_category, id_shop )
ps_category_group, index ON( id_category, id_group )
ps_lang, index ON( id_lang, active )
稍微重写的查询
SELECT
c.id_parent,
c.id_category,
cl.name,
cl.description,
cl.link_rewrite
FROM
ps_category c
INNER JOIN ps_category_lang cl
ON c.id_category = cl.id_category
AND cl.id_shop = 1
AND cl.id_lang = 2
INNER JOIN ps_category_shop cs
ON c.id_category = cs.id_category
AND cs.id_shop = 1
INNER JOIN ps_category_group psg
ON c.id_category = psg.id_category
AND psg.id_group = 1
WHERE
( c.active = 1
OR c.id_category = 2)
AND c.id_category != 1
AND level_depth <= 7
AND nleft >= 350 AND nright <= 351
ORDER BY
level_depth ASC,
cs.position ASC;
第三个查询。请注意，在这种情况下，某些特定的关键元素被移到顶部，因此我也将它们放在键索引中，然后将其余部分放在 where 子句中（主要是可读性调整，但有助于查看“特定”元素指数优势）
SELECT
c.id_category,
cl.name,
cl.link_rewrite
FROM
ps_category c
LEFT JOIN ps_category_lang cl
ON c.id_category = cl.id_category
AND cl.id_shop = 1
INNER JOIN ps_category_shop category_shop
ON c.id_category = category_shop.id_category
AND category_shop.id_shop = 1
WHERE
c.active = 1
AND cl.id_lang = 2
AND c.nleft between 2 and 350
AND c.nright between 351 and 625
AND c.level_depth > 1
ORDER BY
c.level_depth ASC;
您需要确认您真正想要的下一个查询...您对语言表有一个左连接，但是然后在 where 子句中添加“AND l.active = 1”，这实际上会将其变成一个 INNER加入。如果你真的想要一个 LEFT-JOIN，将 l.active 移动到我在这里调整的连接部分
SELECT
l.id_lang,
c.link_rewrite
FROM
ps_category_lang AS c
LEFT JOIN ps_lang AS l
ON c.id_lang = l.id_lang
AND l.active = 1
WHERE
c.id_category = 324
希望这些索引和查询的示例说明/可读性可能有助于改进您的日志。如果其他人仍有问题，请根据需要发布。
修改慢日志报告中的第一个查询
在第一个查询中，您似乎正在从特定产品商店中寻找东西。但是，您从产品类别开始查询，然后左连接到产品，然后再连接到产品商店。由于这些产品最终将通过 where 与特定类别相关联，因此无论如何它都会创建 INNER JOIN。我会稍微重组如下
我会在 ps_product_shop ON ( id_shop, active, visibility, id_product, id_category_default ) 上有一个索引
SELECT
p.*,
ps.*,
stock.out_of_stock,
IFNULL(stock.quantity, 0) as quantity,
MAX(pas.id_product_attribute) id_product_attribute,
pas.minimal_quantity AS product_attribute_minimal_quantity,
pl.description,
pl.description_short,
pl.available_now,
pl.available_later,
pl.link_rewrite,
pl.meta_description,
pl.meta_keywords,
pl.meta_title,
pl.name,
MAX(image_shop.id_image) id_image,
il.legend,
m.name AS manufacturer_name,
cl.name AS category_default,
DATEDIFF(ps.`date_add`, DATE_SUB(NOW(),INTERVAL 20 DAY)) > 0 AS new,
ps.price AS orderprice
FROM
( select @thisLanguage := 1 ) sqlvars,
ps_product_shop ps
INNER JOIN ps_product p
ON ps.id_product = p.id_product
INNER JOIN ps_category_product cp
ON id_product = cp.id_product
AND cp.id_category = 2
LEFT JOIN ps_product_attribute pa
ON p.id_product = pa.id_product
LEFT JOIN ps_product_attribute_shop pas
ON pa.id_product_attribute = pas.id_product_attribute
AND ps.id_shop = pas.id_shop
AND pas.default_on = 1
LEFT JOIN ps_stock_available stock
ON p.id_product = stock.id_product
AND ps.id_shop = stock.id_shop
AND stock.id_shop_group = 0
AND stock.id_product_attribute = IFNULL(pas.id_product_attribute, 0)
LEFT JOIN ps_product_lang pl
ON p.id_product = pl.id_product
AND ps.id_shop = pl.id_shop
AND pl.id_lang = @thisLanguage
LEFT JOIN ps_image i
ON p.id_product = i.id_product
LEFT JOIN ps_image_shop image_shop
ON i.id_image = image_shop.id_image
AND ps.id_shop = image_shop.id_shop
AND image_shop.cover = 1
LEFT JOIN ps_image_lang il
ON image_shop.id_image = il.id_image
AND il.id_lang = @thisLanguage
LEFT JOIN ps_manufacturer m
ON p.id_manufacturer = m.id_manufacturer
LEFT JOIN ps_category_lang cl
ON ps.id_category_default = cl.id_category
AND cl.id_shop = ps.id_shop
AND cl.id_lang = @thisLanguage
WHERE
ps.id_shop = 1
AND ps.active = 1
AND ps.visibility IN ("both", "catalog")
GROUP BY
ps.id_product
ORDER BY
cp.position ASC
LIMIT
0,8;
至于将多字段索引创建为单个索引，例如：
CREATE INDEX act_id_lang ON ps_category(active, id_category, id_lang, nleft, nright, level_depth);
给出一个简单的索引名称......在任何表上......使用所有键，因为它们将在查询中有效。