两个表之间的SQLite CASE

Question

两个表之间的SQLite CASE
我有2个表格“主题”和“子”

表格主题：

+------------+-------------+
| id_topic   | topic_name  |
+------------+-------------+
| 1          | books       |
| 2          | food        |
| 3          | movies      |
| 4          | weather     |
| 5          | travel      |
| 6          | pets        |
+------------+-------------+

TABLE SUB：

+------------+
| id_topic   |
+------------+
| 2          |
| 5          |
+------------+

我要打印这个：

+-------------+-------------+-------------+
| id_topic    | topic_name  | subscribed  |
+-------------+-------------+-------------+
| 1           | books       | no          |
| 2           | food        | yes         |
| 3           | movies      | no          |
| 4           | weather     | no          |
| 5           | travel      | yes         |
| 6           | pets        | no          |
+-------------+-------------+-------------+

Answer 1

您需要一个left join和一个CASE语句：

select 
  t.*,
  case 
    when s.id_topic is null then 'no'
    else 'yes'
  end subscribed
from topics t left join sub s
on s.id_topic = t.id_topic