Pivot MySQL 表设置 boolean 值

Question

I have to perform what I think is a very basic MYSQL table pivot, but I am completely new to sql so I am not sure about the syntax. I have the following table

record_id tag_id
id_1      tag1
id_1      tag2
id_2      tag1
id_2      tag3

I would like to obtain a pivoted table, whose rows are the unique record_ids, the columns are the unique tag_ids, and the values are boolean true/false if that record_id has that tag. In this case, the expected result would be:

record_id tag1  tag2  tag3
id_1      true  true  false
id_2      true  false true

How can I achieve this?

Further question: what if I have another table that associates tag_names to tag_id, and I would like the columns of my pivoted table to be named after tag_names? In this example, starting from

tag_id tag_name
tag1   tag_name1
tag2   tag_name2
tag3   tag_name3

I would finally get

record_id tag_name1  tag_name2  tag_name3
id_1      true       true       false
id_2      true       false      true

I appreciate any help.

Answer 1

SELECT record_id,
       CASE WHEN SUM(tag_id = 'tag1') THEN 'true' ELSE 'false' END tag1,
       CASE WHEN SUM(tag_id = 'tag2') THEN 'true' ELSE 'false' END tag2,
       CASE WHEN SUM(tag_id = 'tag3') THEN 'true' ELSE 'false' END tag3
FROM source_table
GROUP BY record_id
ORDER BY record_id