SQL 多个左连接作为新列的性能

Question

我有 3 张桌子：

账户

id	name
1	Google
2	Apple

custom_field

id	name
1	Phone
2	Email

custom_field_submission

id	custom_field_id	entity_id	value
1	1	1	555-444-333
2	1	2	111-111-111
3	2	1	google@goog.com
4	2	2	apple@apple.com

查询后的预期结果

id	name	Phone	Email
1	Google	555-444-333	google@goog.com
2	Apple	111-111-111	apple@apple.com

我有这样的查询：

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

实际上我有 10000 个帐户的 20 个自定义字段。我在哪里运行查询很慢（3-4 秒）

你有管理优化这个的想法吗？

谢谢。

Answer 1

这里你需要的是一个数据透视查询：

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;

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