returning rows based on some criteria and if no row match the criteria then return all rows in mariadb sql

Question

I am trying to fetch rows based on some criteria here. What I want is to get the rows if the rows available with matching criteria AND if does not match then return all rows.

Below is my query.

SELECT t.* FROM 
        CASE 
        WHEN (SELECT COUNT(*) FROM users WHERE user_name LIKE '%10%' > 0) 
        // Line 3       
        THEN
           (SELECT * FROM users WHERE user_name LIKE '%10%' LIMIT 0,10)t
        ELSE 
           (SELECT * FROM users LIMIT 0,10)t   
        END

I am getting syntax error at line 3

Answer 1

you can use mariadb if-then-else statement

   IF (SELECT COUNT(*) FROM users WHERE user_name LIKE '%10%') > 0
      SELECT * FROM users WHERE user_name LIKE '%10%' LIMIT 0,10
   ELSE
      SELECT * FROM users WHERE user_name
   END IF;

Answer 2

You can use UNION ALL :

(SELECT u.*
 FROM users u
 WHERE u.user_name LIKE '%10%'
 LIMIT 0, 10
) UNION ALL
(SELECT u.*
 FROM users u
 WHERE NOT EXISTS (SELECT 1 FROM users u2 WHERE u2.user_name LIKE '%10%')
 LIMIT 0, 10
) ;

You can also just use OR :

SELECT u.*
FROM users u
WHERE u.user_name LIKE '%10%' OR
      NOT EXISTS (SELECT 1 FROM users u2 WHERE u2.user_name LIKE '%10%')
LIMIT 0, 10