[英]Query with OR making query execution SLOW
我是新手,或遇到OR查詢問題!
當我不使用OR進行操作時,執行時間為:0.02秒
SELECT DISTINCT p.*,
ht.html_title,
ht.html_content,
sc.sub_cat_name,
sc.main_cat_id,
us.username,
c.name AS cityname
FROM ad_product p,
ad_html ht,
ad_catagory_sub sc,
ad_user us,
ad_cities c
WHERE ( ht.ad_id = p.id )
AND ( sc.sub_cat_id = p.category )
AND ( us.id = p.user_id )
AND ( p.category = 216 )
AND ( p.status = 'active' )
AND ( c.id = p.city )
AND ( p.city = 135 )
ORDER BY p.created_at DESC;
當我在OR條件下嘗試時,大約需要4.70秒
SELECT DISTINCT p.*,
ht.html_title,
ht.html_content,
sc.sub_cat_name,
sc.main_cat_id,
us.username,
c.name AS cityname
FROM ad_product p,
ad_html ht,
ad_catagory_sub sc,
ad_user us,
ad_cities c
WHERE ( ht.ad_id = p.id )
AND ( sc.sub_cat_id = p.category )
AND ( us.id = p.user_id )
AND ( p.category = 216
OR p.parent_category = 216 )
AND ( p.status = 'active' )
AND ( c.id = p.city )
AND ( p.city = 135 )
ORDER BY p.created_at DESC;
說明:
+----+-------------+-------+------------+-------------+--------------------------------------------------------------------------------+--------------------------+---------+---------------------------+-------+----------+----------------------------------------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+-------+------------+-------------+--------------------------------------------------------------------------------+--------------------------+---------+---------------------------+-------+----------+----------------------------------------------------+
| 1 | SIMPLE | c | NULL | const | PRIMARY | PRIMARY | 4 | const | 1 | 100.00 | Using temporary; Using filesort |
| 1 | SIMPLE | p | NULL | index_merge | PRIMARY,id,parent_category,city,user_id_2,category,status,id_2,id_3,category_2 | category,parent_category | 4,4 | NULL | 67889 | 4.74 | Using union(category,parent_category); Using where |
| 1 | SIMPLE | sc | NULL | eq_ref | PRIMARY | PRIMARY | 4 | abc_classified.p.category | 1 | 100.00 | NULL |
| 1 | SIMPLE | us | NULL | eq_ref | PRIMARY | PRIMARY | 4 | abc_classified.p.user_id | 1 | 100.00 | NULL |
| 1 | SIMPLE | ht | NULL | ref | ad_id | ad_id | 4 | abc_classified.p.id | 1 | 100.00 | NULL |
+----+-------------+-------+------------+-------------+--------------------------------------------------------------------------------+--------------------------+---------+---------------------------+-------+----------+----------------------------------------------------+
我認為我已經定義了適當的索引,有人可以指出我做錯了什么嗎? 或如何減少執行時間? 另外,據我所知為什么會發生這種情況?
我認為您的查詢將從聯合而不是or中受益。 這將創建2組數據。 一個在categoryid上,另一個在父categoryid上。 這比定義2個否定集要快。 一組沒有categoryid = 216的集合,而另一組沒有父categoryid = 216的集合。
SELECT DISTINCT p1.*,
ht.html_title,
ht.html_content,
sc.sub_cat_name,
sc.main_cat_id,
us.username,
c.name AS cityname
FROM ad_product p1 inner join ad_html ht on ht.ad_id = p1.id
inner join ad_category_sub sc on sc.sub_cat_id = p1.category
inner join ad_user us on us.id = p1.user_id
inner join ad_cities c on c.id = p1.city
WHERE ( p1.status = 'active' )
AND ( p1.city = 135 )
AND ( p1.category = 216)
UNION
SELECT DISTINCT p.*,
ht.html_title,
ht.html_content,
sc.sub_cat_name,
sc.main_cat_id,
us.username,
c.name AS cityname
FROM ad_product p
inner join ad_html ht on ht.ad_id = p.id
inner join ad_category_sub sc on sc.sub_cat_id = p.category
inner join ad_user us on us.id = p.user_id
inner join ad_cities c on c.id = p.city
WHERE ( p.status = 'active' )
AND ( p.city = 135 )
AND (p.parent_category = 216)
ORDER BY p.created_at DESC;
@Dwight Reynoldson Answers在SQL Server上工作正常,我在MySQL上遇到了“ ORDER BY”問題的解決方法。 我所做的只是由ORDER BY created_at DESC
而不是ORDER BY p.created_at DESC
造成所有問題的是p。
回答:
SELECT DISTINCT p1.*,
ht.html_title,
ht.html_content,
sc.sub_cat_name,
sc.main_cat_id,
us.username,
c.name AS cityname
FROM ad_product p1 inner join ad_html ht on ht.ad_id = p1.id
inner join ad_category_sub sc on sc.sub_cat_id = p1.category
inner join ad_user us on us.id = p1.user_id
inner join ad_cities c on c.id = p1.city
WHERE ( p1.status = 'active' )
AND ( p1.city = 135 )
AND ( p1.category = 216)
UNION
SELECT DISTINCT p.*,
ht.html_title,
ht.html_content,
sc.sub_cat_name,
sc.main_cat_id,
us.username,
c.name AS cityname
FROM ad_product p
inner join ad_html ht on ht.ad_id = p.id
inner join ad_category_sub sc on sc.sub_cat_id = p.category
inner join ad_user us on us.id = p.user_id
inner join ad_cities c on c.id = p.city
WHERE ( p.status = 'active' )
AND ( p.city = 135 )
AND (p.parent_category = 216)
ORDER BY created_at DESC;
當您在where條件中定義精確值時,SQL使用hash join
聯接。 因此,它比其他聯接要快得多。 當您將其更改為非精確值條件(X或Y)時,它變慢。
解決方案是建立index
,以減少要搜索的記錄。
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