MySQL根据第三个查询的结果运行两个sql查询之一

Question

I have three sql queries:

1) SELECT * FROM table_name_1 WHERE user = 'user1' AND sub_name = '' AND name != 'some_name'; 
2) SELECT * FROM table_name_1 WHERE user = 'user1' AND sub_name = ''; 
3) SELECT DISTINCT role FROM table_name_1 where user = 'user1';

Here, can I combine these 3 queries to be able to run either query 1 or query 2 depending on result of query 3?

I can run query 3 first and take that output in a variable and depending on the value in that varaible can run either query 1 or 2. But I want to see if all this can be done purely in sql.

I tried it using IF but getting error as below, which I think is because I am not selecting any column after first SELECT. But I don't really need anything selected there:

mysql> SELECT IF(((select distinct role from table_name_1 where user = 'user1') = 'admin'),(SELECT name, display, good_high, critical_low, warning_low, warning_high FROM table_name_1 WHERE user = 'user1' AND sub_name = ''),(SELECT name, display, good_high, critical_low, warning_low, warning_high FROM table_name_1 WHERE user = 'user1' AND sub_name = '' AND name != 'some_name')); 
ERROR 1241 (21000): Operand should contain 1 column(s) 


mysql> SELECT IF(((select role from table_name_1 where user = 'user1' limit 1) = 'admin'),(SELECT name, display, good_high, critical_low, warning_low, warning_high FROM table_name_1 WHERE user = 'user1' AND sub_name = ''),(SELECT name, display, good_high, critical_low, warning_low, warning_high FROM table_name_1 WHERE user = 'user1' AND sub_name = '' AND name != 'some_name')); 
ERROR 1241 (21000): Operand should contain 1 column(s) 
mysql>

Answer 1

You can combine those queries with EXISTS:

SELECT *
FROM table_name_1
WHERE
  user = 'user1'
  AND sub_name = ''
  AND (
   (name != 'some_name')
   OR EXISTS (SELECT role FROM table_name_1
              WHERE user = 'user1' AND role='admin')
  )