How to join two tables to find two conditions?

Question

So I am trying to list all of the names and ages of people who have not visited the same bar that Ashley has visited.

I currently have two tables: Visits and Drinkers

Drinkers:

`DLicNO     DName     DCity         Age 
AK117229    Ashley    Honolulu      53  
UU761336    Joe       Chicago       51  
ZM193312    Mike      Wilmington    72  
MD891129    Clark     St.Louis      62  
YU134618    Johnson   St.Louis      61  `

Visits:

`DLicNo     BNO        NumberOfTimes    
AK117229    L22174     7    
MD891129    L59871     1    
AK117229    L59871     2    
UU761326    L31927     8    
YU134618    L31927     8    
ZM193312    L889109    6`

I attempted to join them doing this:

SELECT DName, Age 
FROM  visits V, drinkers D 
WHERE V.DLicNo != (
    SELECT DLicNo  
    FROM visits 
    WHERE DLicNo = 'AK117229' 
) 
AND V.DLicNo = D.DLicNO;

I just feel as if I am doing something wrong in the.= condition. Any help would be greatly appreciated.

Answer 1

Use This Two Method:

SELECT 
 DName, 
 Age 
FROM  
   visits V JOIN drinkers D  ON (V.DLicNo =D.DLicNO AND  V.DLicNo != 'AK117229')

OR

SELECT 
  DName, 
  Age 
FROM  
  visits V JOIN  drinkers D ON V.DLicNo =D.DLicNO 
WHERE   
  V.DLicNo != 'AK117229'

Answer 2

You need to figure out the combinations of other drinkers with Ashley in each bar and count them, only showing the results where the count is 0 (ie that person has not drunk in the same bar as Ashley ):

SELECT d1.DName, d1.Age
FROM visits v1
JOIN drinkers d1 ON d1.DLicNO = v1.DLicNO AND d1.DName != 'Ashley'
JOIN visits v2 ON v1.BNO = v2.BNO
LEFT JOIN drinkers d2 ON d2.DLicNO = v2.DLicNO AND d2.DName = 'Ashley'
GROUP BY d1.DName, d1.Age
HAVING COUNT(d2.DLicNO) = 0

Output:

DName       Age
Joe         51
Johnson     61
Mike        72

Demo on dbfiddle

Answer 3

You are right about ".=", Generally speaking. you have to use "NOT IN (select..,)". but in your case you do not need that extra "SELECT": This is the right form:

SELECT DName, Age 
FROM  visits V JOIN drinkers D ON V.DLicNo = D.DLicNO
WHERE V.DLicNo != 'AK117229';

Answer 4

I guess you need to do something like below:

SELECT DName, AGE FROM Drinkers D INNER JOIN visits V ON D.DLicNo = V.DLicNo WHERE V.BNO NOT IN 
   (SELECT V1.BNO  
    FROM visits V1
    WHERE V1.DLicNo = 'AK117229')

It is simple and short and easy to understand

Here is the working fiddle

Answer 5

You can try with CTE option. It is tested in MYSQL 8.0 Version, where CTE was introducted. Read more on Common Table Expressions in MySQL

WITH ashleybars as
(
  SELECT BNO
  FROM visits
  WHERE DLicNo = 'AK117229'
), otherpersonsOfsamebar as 
(
  select distinct DLicNo
  from visits as v inner join ashleybars as b
  where v.bno = b.bno
  )
  select * from drinkers
  where DLicNo NOT IN (select DLicNo FROM otherpersonsOfsamebar);