SQL-将select *查询与select 1组合

Question

I'm trying to combine data from two tables in one result. With simplified example-tables, this is what I want to get in result:

ID    Text                Choice
--------------------------------
1     My first choice     0
2     My second choice    0
3     My third choice     1

from the two tables persons and choosen

'Persons':

ID      Name    Age
-------------------
1       Adam    22
2       Scott   25
3       Tom     28

'Choices':

ID    Text
----------------------
1     My first choice
2     My second choice
3     My third choice

'Choices_made':

Person_ID    Choice_ID
----------------------
2            3

I have tried some different queries, but not found the right one. I got stuck when trying this query:

SELECT * FROM (
(SELECT * FROM Choices) t1
UNION
(SELECT 1 as Choice FROM Choices_made WHERE Person_ID=2) t2
) t_union

... which does not work. It causes error #1064 - You have an error in your SQL syntax.

Any suggestions on how I can accomplish the wanted result?

Answer 1

You can try the next query

SELECT Choices.*
      ,IF(Choices_made.Choice_ID IS NULL, 0, 1) AS Choice
FROM Choices
     LEFT JOIN Choices_made ON Choices_made.Choice_ID = Choices.ID AND Choices_made.Person_ID = @PersonID

Answer 2

SELECT c.id,
       c.text, 
       cm.Choice_ID = c.id as persons_choice
FROM Choices c
LEFT JOIN Choices_made cm on cm.Choice_ID = c.id
                         and cm.Person_ID = 2

Answer 3

You could use left join then use case when when setting the 3rd field to 1 or zero

SELECT p.id as , c.text, 
CASE 
WHEN cm.choice_id <> 0 then 1
ELSE 
0
END
as Choice
from persons as p
left join choices as c on c.id = p.id
left join choices_made as cm on cm.personid = p.id