MySql Join a View Table as a Boolean

Question

I have a users table, and a view table which lists some user ids... They look something like this:

Users:

User_ID  |   Name       |   Age   | ...
   555      John Doe        35
   556      Jane Doe        24
   557      John Smith      18

View_Table

User_ID
  555
  557

Now, when I do run a query to retrieve a user:

SELECT User_ID,Name,Age FROM Users WHERE User_ID = 555

SELECT User_ID,Name,Age FROM Users WHERE User_ID = 556

I also would like to select a boolean, stating whether or not the user I'm retrieving is present in the View_Table.

Result:

   User_ID           Name          Age      In_View
    555             John Doe       35         1
    556             Jane Doe       24         0

Any help would be greatly appreciated. Efficiency is a huge plus. Thanks!!

Answer 1

SELECT Users.User_ID,Name,Age, View_Table.User_ID IS NOT NULL AS In_View
FROM Users 
LEFT JOIN View_table USING (User_ID)
WHERE User_ID = 555

Answer 2

SELECT 
   User_ID, Name, Age, 
   CASE WHEN v.UserID is not null THEN 1 ELSE 0 END AS In_View
FROM Users u
LEFT JOIN View_Table v on u.User_ID = v.UserID
WHERE UserID ...;

Answer 3

I would do a LEFT JOIN . So long as you have key/index for User_ID , it should be very efficient.

SELECT User_ID,Name,Age, IF(View_Table.User_ID, 1, 0) AS In_View
FROM Users LEFT JOIN View_Table USING(User_ID)
WHERE User_ID = 555

Answer 4

I know this is an "Old" question but just happened upon this and none of these answers seemed to be that good. So I thought I would throw in my 2 cents

SELECT
    u.User_ID,
    u.Name,
    u.Age,
    COALESCE((SELECT 1 FROM View_Table AS v WHERE v.User_ID = u.User_ID ), 0) AS In_View
FROM
    Users AS u
WHERE
    u.User_ID = 555

Simply select 1 with a correlated query ( or null ) then to get the 0 we can use the handy function COALESCE which returns the first non-null value left to right.