[英]Optimize MySQL self-join query
我有包含重復行的c_regs表。 我在form_number和property_name列上創建了索引。 不幸的是,這個查詢仍然需要很長時間才能完成,特別是添加了t10和t11連接。 有沒有辦法優化它? 謝謝。
select
ifnull(x.form_datetime,'') reg_date,
ifnull(x.property_value,'') amg_id,
x.form_number,
x.form_name,
x.form_version,
ifnull(t1.property_value,'') first_name,
ifnull(t2.property_value,'') last_name,
ifnull(t3.property_value,'') address,
ifnull(t4.property_value,'') address_2,
ifnull(t5.property_value,'') city,
ifnull(t6.property_value,'') state_code,
ifnull(t7.property_value,'') zip,
ifnull(t8.property_value,'') phone,
ifnull(t9.property_value,'') email,
ifnull(t10.property_value,'') registrant_type,
t11.property_value auth_type_code
from
(select distinct form_datetime, form_number, form_name, form_version, property_value from c_regs where property_name = 'field.frm_personID') as x
inner join (select distinct * from c_regs) as t1 on t1.form_number = x.form_number and t1.property_name = 'field.frm_firstName'
inner join (select distinct * from c_regs) as t2 on t2.form_number = x.form_number and t2.property_name = 'field.frm_lastName'
inner join (select distinct * from c_regs) as t3 on t3.form_number = x.form_number and t3.property_name = 'field.frm_address'
left join (select distinct * from c_regs) as t4 on t4.form_number = x.form_number and t4.property_name = 'field.frm_address2'
inner join (select distinct * from c_regs) as t5 on t5.form_number = x.form_number and t5.property_name = 'field.frm_city'
inner join (select distinct * from c_regs) as t6 on t6.form_number = x.form_number and t6.property_name = 'field.frm_state'
inner join (select distinct * from c_regs) as t7 on t7.form_number = x.form_number and t7.property_name = 'field.frm_zip'
inner join (select distinct * from c_regs) as t8 on t8.form_number = x.form_number and t8.property_name = 'field.frm_phone'
inner join (select distinct * from c_regs) as t9 on t9.form_number = x.form_number and t9.property_name = 'field.frm_emailAddress'
left join (select distinct * from c_regs) as t10 on t10.form_number = x.form_number and t10.property_name = 'field.frm_youAre'
inner join (select distinct * from c_regs) as t11 on t11.form_number = x.form_number and t11.property_name = 'field.frm_authType'
;
您不應該一直使用SELECT DISTINCT
。 請記住,如果您的選擇列表中有任何唯一約束,則DISTINCT必然是無操作,因此可能沒有必要。 如果存在重復,則DISTINCT成本很高,因為它對表進行排序,因此重復排列在一起以進行去除。
您也不應該為此類數據進行大量自連接。 自聯接中的每個子查詢都在讀取整個表。
SELECT form_number,
MAX(form_datetime) AS reg_date,
MAX(form_name) AS form_name,
MAX(form_version) AS form_version,
MAX(CASE property_name WHEN 'field.frm_personID' THEN property_value END) AS amg_id,
MAX(CASE property_name WHEN 'field.frm_firstName' THEN property_value END) AS first_name,
MAX(CASE property_name WHEN 'field.frm_lastName' THEN property_value END) AS last_name,
MAX(CASE property_name WHEN 'field.frm_address' THEN property_value END) AS address,
MAX(CASE property_name WHEN 'field.frm_address2' THEN property_value END) AS address_2,
MAX(CASE property_name WHEN 'field.frm_city' THEN property_value END) AS city,
MAX(CASE property_name WHEN 'field.frm_state' THEN property_value END) AS state_code,
MAX(CASE property_name WHEN 'field.frm_zip' THEN property_value END) AS zip,
MAX(CASE property_name WHEN 'field.frm_phone' THEN property_value END) AS phone,
MAX(CASE property_name WHEN 'field.frm_emailAddress' THEN property_value END) AS email,
MAX(CASE property_name WHEN 'field.frm_youAre' THEN property_value END) AS registrant_type,
MAX(CASE property_name WHEN 'field.frm_authType' THEN property_value END) AS auth_type_code
FROM c_regs
GROUP BY form_number;
說明: GROUP BY
導致給定form_number的所有行都被視為一個組,結果每個組將有一行。
GROUP BY
中未命名的所有其他列必須位於分組函數中。 我選擇了MAX()。 我假設表單日期時間,名稱和版本每個組應該只有一個不同的值。
對於屬性,我們在MAX()函數中放置一個表達式,僅在屬性具有特定值的行上返回值。 在其他行上,表達式為NULL,MAX()將忽略該表達式。
通過這種方式,您可以獲得所需的結果,而無需執行任何自連接或DISTINCT修改器。 查詢只掃描一次表,它應該更快。
BK認為許多自我聯合是有害的,這是一種誤導。
考慮包含10,000個實體的EAV數據集,每個實體具有12個屬性,如下所示:
DROP TABLE IF EXISTS my_table;
CREATE TABLE my_table
(entity INT NOT NULL
,attribute INT NOT NULL
,value INT NOT NULL
,PRIMARY KEY(entity,attribute)
);
INSERT INTO my_table VALUES
(1,101,RAND()*100),
(1,102,RAND()*100),
(1,103,RAND()*100),
(1,104,RAND()*100),
(1,105,RAND()*100),
(1,106,RAND()*100),
(1,107,RAND()*100),
(1,108,RAND()*100),
(1,109,RAND()*100),
(1,110,RAND()*100),
(1,111,RAND()*100),
(1,112,RAND()*100);
使用這個初始種子,我可以使用整數表(0-9)來快速填充表格的其余部分......
INSERT IGNORE INTO my_table SELECT i4.i*1000+i3.i*100+i2.i*10+i1.i+1, attribute, RAND()*100 FROM my_table,ints i1, ints i2, ints i3, ints i4;
比爾的詢問......
SELECT SQL_NO_CACHE a.entity
, MAX(CASE WHEN attribute = 101 THEN value END) x101
, MAX(CASE WHEN attribute = 102 THEN value END) x102
, MAX(CASE WHEN attribute = 103 THEN value END) x103
, MAX(CASE WHEN attribute = 104 THEN value END) x104
, MAX(CASE WHEN attribute = 105 THEN value END) x105
, MAX(CASE WHEN attribute = 106 THEN value END) x106
, MAX(CASE WHEN attribute = 107 THEN value END) x107
, MAX(CASE WHEN attribute = 108 THEN value END) x108
, MAX(CASE WHEN attribute = 109 THEN value END) x109
, MAX(CASE WHEN attribute = 110 THEN value END) x110
, MAX(CASE WHEN attribute = 111 THEN value END) x111
, MAX(CASE WHEN attribute = 112 THEN value END) x112
FROM my_table a
GROUP
BY a.entity;
+--------+------+------+------+------+------+------+------+------+------+------+------+------+
| entity | x101 | x102 | x103 | x104 | x105 | x106 | x107 | x108 | x109 | x110 | x111 | x112 |
+--------+------+------+------+------+------+------+------+------+------+------+------+------+
| 1 | 78 | 8 | 4 | 95 | 66 | 43 | 16 | 51 | 9 | 89 | 20 | 33 |
...
| 9998 | 61 | 72 | 67 | 20 | 23 | 10 | 31 | 37 | 69 | 18 | 24 | 32 |
| 9999 | 67 | 91 | 32 | 58 | 77 | 81 | 61 | 22 | 75 | 65 | 91 | 42 |
| 10000 | 52 | 38 | 56 | 32 | 14 | 77 | 10 | 99 | 70 | 70 | 82 | 13 |
+--------+------+------+------+------+------+------+------+------+------+------+------+------+
10000 rows in set (0.20 sec)
另類......
SELECT SQL_NO_CACHE a.entity
, a.value x101
, b.value x102
, c.value x103
, d.value x104
, e.value x105
, f.value x106
, g.value x107
, h.value x108
, i.value x109
, j.value x110
, k.value x111
, l.value x112
FROM my_table a
LEFT JOIN my_table b ON b.entity = a.entity AND b.attribute = 102
LEFT JOIN my_table c ON c.entity = a.entity AND c.attribute = 103
LEFT JOIN my_table d ON d.entity = a.entity AND d.attribute = 104
LEFT JOIN my_table e ON e.entity = a.entity AND e.attribute = 105
LEFT JOIN my_table f ON f.entity = a.entity AND f.attribute = 106
LEFT JOIN my_table g ON g.entity = a.entity AND g.attribute = 107
LEFT JOIN my_table h ON h.entity = a.entity AND h.attribute = 108
LEFT JOIN my_table i ON i.entity = a.entity AND i.attribute = 109
LEFT JOIN my_table j ON j.entity = a.entity AND j.attribute = 110
LEFT JOIN my_table k ON k.entity = a.entity AND k.attribute = 111
LEFT JOIN my_table l ON l.entity = a.entity AND l.attribute = 112
WHERE a.attribute = 101;
+--------+------+------+------+------+------+------+------+------+------+------+------+------+
| entity | x101 | x102 | x103 | x104 | x105 | x106 | x107 | x108 | x109 | x110 | x111 | x112 |
+--------+------+------+------+------+------+------+------+------+------+------+------+------+
| 1 | 78 | 8 | 4 | 95 | 66 | 43 | 16 | 51 | 9 | 89 | 20 | 33 |
...
| 9998 | 61 | 72 | 67 | 20 | 23 | 10 | 31 | 37 | 69 | 18 | 24 | 32 |
| 9999 | 67 | 91 | 32 | 58 | 77 | 81 | 61 | 22 | 75 | 65 | 91 | 42 |
| 10000 | 52 | 38 | 56 | 32 | 14 | 77 | 10 | 99 | 70 | 70 | 82 | 13 |
+--------+------+------+------+------+------+------+------+------+------+------+------+------+
10000 rows in set (0.23 sec)
因此,Bill的查詢速度要快一些。 但是,只要減少所尋求的實體數量(同時保持相同數量的屬性 - 連接數相同),替代查詢就可以通過接近相同類型的邊界來超越Bill's ...
Bill的查詢添加了WHERE a.entity <= 5000
| 4998 | 59 | 55 | 93 | 48 | 72 | 32 | 38 | 36 | 6 | 82 | 23 | 62 |
| 4999 | 23 | 10 | 11 | 29 | 69 | 67 | 92 | 72 | 25 | 49 | 79 | 48 |
| 5000 | 39 | 86 | 77 | 0 | 30 | 38 | 48 | 54 | 9 | 97 | 25 | 54 |
+--------+------+------+------+------+------+------+------+------+------+------+------+------+
5000 rows in set (0.12 sec)
添加WHERE a.entity <= 5000
的替代方案
| 4998 | 59 | 55 | 93 | 48 | 72 | 32 | 38 | 36 | 6 | 82 | 23 | 62 |
| 4999 | 23 | 10 | 11 | 29 | 69 | 67 | 92 | 72 | 25 | 49 | 79 | 48 |
| 5000 | 39 | 86 | 77 | 0 | 30 | 38 | 48 | 54 | 9 | 97 | 25 | 54 |
+--------+------+------+------+------+------+------+------+------+------+------+------+------+
5000 rows in set (0.11 sec)
所以它實際上不是連接的數量,而是刻苦使用索引,這使得查詢之間存在差異和快速查詢。
你不需要所有這些連接。 通過我的優化,數據將按行而不是列返回。
(我沒有運行這個,所以先測試一下)
SELECT
ifnull(x.form_datetime,'') reg_date,
ifnull(x.property_value,'') amg_id,
x.form_number,
x.form_name,
x.form_version,
x.property_name,
x.property_value
FROM c_regs x
WHERE x.property_name IN (
'field.frm_firstName',
'field.frm_lastName',
'field.frm_address',
...
)
AND x.form_number = 'the form id'
GROUP BY x.form_number, x.property_name
ORDER BY x.form_number ASC;
僅當您需要特定表單時才需要AND
,而不是所有表單。 (我建議)
還問自己一個問題:你是否需要在條件中擁有字段名稱? 您可以將我的查詢用作子查詢,然后像以前一樣將每個字段合並為列,而無需另一個連接。
嘗試在代碼中添加union子句
喜歡
SELECT ID, NAME, AMOUNT, DATE
FROM CUSTOMERS
LEFT JOIN ORDERS
ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID
UNION
SELECT ID, NAME, AMOUNT, DATE
FROM CUSTOMERS
RIGHT JOIN ORDERS
ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID;
這太可怕了:
inner join (select distinct * from c_regs) as t7
on t7.form_number = x.form_number and t7.property_name = 'field.frm_zip'
它掃描整個c_regs
表,刪除重復的行,並將重復刪除的行復制到沒有索引的臨時表中。 然后它在其中搜索可能( 或可能不是 )一行的內容。
請注意, DISTINCT
並不保證最多一行將被退回。 (我會忽略多行問題。)
這樣做會好得多
inner join c_regs AS t7 ON
t7.form_number = x.form_number and t7.property_name = 'field.frm_zip'
但是這也需要INDEX(form_number, property_name)
。 更好的方法是讓PRIMARY KEY
從這兩列開始,如下所述: http : //mysql.rjweb.org/doc.php/index_cookbook_mysql#speeding_up_wp_postmeta
同時,在第一個FROM之后不需要額外的SELECT層。
同時,你應該開始擺脫c_regs中的重復, 並阻止他們返回! 合適的自然PRIMARY KEY
可能解決問題。 (再次,請參閱我的鏈接。)
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