SQL 多個左連接作為新列性能

Question

我有 3 張桌子：

帳戶

ID	姓名
1	谷歌
2	蘋果

自定義字段

ID	姓名
1	電話
2	Email

custom_field_submission

ID	custom_field_id	entity_id	價值
1	1	1	555-444-333
2	1	2	111-111-111
3	2	1	google@goog.com
4	2	2	蘋果@apple.com

查詢后的預期結果

ID	姓名	電話	Email
1	谷歌	555-444-333	google@goog.com
2	蘋果	111-111-111	蘋果@apple.com

我有一個這樣的查詢：

SELECT
a.id,
a.name,
phone.value as phone,
email.value as email

FROM account a

LEFT JOIN ( 
  SELECT DISTINCT custom_field_submission.value, custom_field_submission.entity_id
  FROM custom_field_submission
  WHERE custom_field_submission.custom_field_id = 1) AS phone 
ON phone.entity_id = a.id

LEFT JOIN ( 
  SELECT DISTINCT custom_field_submission.value, custom_field_submission.entity_id
  FROM custom_field_submission
  WHERE custom_field_submission.custom_field_id = 2) AS email 
ON email.entity_id = a.id

實際上，我為 10 000 個帳戶提供了 20 個自定義字段。 我在哪里運行查詢非常慢（3-4秒）

你有一個想法來管理優化這個嗎？

謝謝。

Answer 1

您需要的是 pivot 查詢：

SELECT
    a.id,
    a.name,
    MAX(CASE WHEN cf.name = 'Phone' THEN cfs.value END) AS Phone,
    MAX(CASE WHEN cf.name = 'Email' THEN cfs.value END) AS Email
FROM account a
LEFT JOIN custom_field_submission cfs
    ON cfs.entity_id = a.id
LEFT JOIN custom_field cf
    ON cf.id = cfs.custom_field_id
GROUP BY
    a.id,
    a.name;