为什么限制0,1比限制0、17慢

我正在尝试分析为什么以下查询速度较慢 LIMIT 0,1比LIMIT 0,100

我已经添加 SQL_NO_CACHE用于测试目的。

询问：

 SELECT 
  SQL_NO_CACHE  SQL_CALC_FOUND_ROWS wp_posts.*, 
  low_stock_amount_meta.meta_value AS low_stock_amount
FROM 
  wp_posts 
  LEFT JOIN wp_wc_product_meta_lookup wc_product_meta_lookup ON wp_posts.ID = wc_product_meta_lookup.product_id 
  LEFT JOIN wp_postmeta AS low_stock_amount_meta ON wp_posts.ID = low_stock_amount_meta.post_id 
  AND low_stock_amount_meta.meta_key = '_low_stock_amount' 
WHERE 
  1 = 1 
  AND wp_posts.post_type IN ('product', 'product_variation') 
  AND (
    (wp_posts.post_status = 'publish')
  ) 
  AND wc_product_meta_lookup.stock_quantity IS NOT NULL 
  AND wc_product_meta_lookup.stock_status IN('instock', 'outofstock') 
  AND (
    (
      low_stock_amount_meta.meta_value > '' 
      AND wc_product_meta_lookup.stock_quantity <= CAST(
        low_stock_amount_meta.meta_value AS SIGNED
      )
    ) 
    OR (
      (
        low_stock_amount_meta.meta_value IS NULL 
        OR low_stock_amount_meta.meta_value <= ''
      ) 
      AND wc_product_meta_lookup.stock_quantity <= 2
    )
  ) 

ORDER BY 
  wp_posts.ID DESC 
LIMIT 
  0, 1

解释显示完全相同的输出

1   SIMPLE  wp_posts    index   PRIMARY,type_status_date    PRIMARY 8   NULL    27071   Using where
1   SIMPLE  low_stock_amount_meta   ref post_id,meta_key    meta_key    767 const   1   Using where
1   SIMPLE  wc_product_meta_lookup  eq_ref  PRIMARY,stock_status,stock_quantity,product_id  PRIMARY 8   woocommerce-admin.wp_posts.ID   1   Using where

平均查询时间为 350ms LIMIT 0,1

平均查询时间为 7ms LIMIT 0,100

查询性能开始变得更快 LIMIT 0,17

我已经按照这个问题中的建议在 order by 子句中添加了另一列，但这会Using filesort在解释输出中触发

Order by wp_posts.post_date, wp_posts.ID desc

1   SIMPLE  wp_posts    ALL PRIMARY,type_status_date    NULL    NULL    NULL    27071   Using where; Using filesort
1   SIMPLE  low_stock_amount_meta   ref post_id,meta_key    meta_key    767 const   1   Using where
1   SIMPLE  wc_product_meta_lookup  eq_ref  PRIMARY,stock_status,stock_quantity,product_id  PRIMARY 8   woocommerce-admin.wp_posts.ID   1   Using where

有没有办法在不改变索引的情况下解决它，为什么会发生这种情况？

同样有趣的是，查询时间从LIMIT 0,17. 我不确定为什么 17 在这里是一个神奇的数字。

更新 1：我刚刚尝试添加FORCE INDEX(PRIMARY)，现在LIMIT 0,100具有与LIMIT 0,1smh相同的性能