SQL 多个左连接作为新列性能

Question

我有 3 张桌子：

帐户

ID	姓名
1	谷歌
2	苹果

自定义字段

ID	姓名
1	电话
2	Email

custom_field_submission

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

查询后的预期结果

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

我有一个这样的查询：

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

实际上，我为 10 000 个帐户提供了 20 个自定义字段。 我在哪里运行查询非常慢（3-4秒）

你有一个想法来管理优化这个吗？

谢谢。

Answer 1

您需要的是 pivot 查询：

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;