如果第一个结果集为空，则SQL UNION不显示第二个结果集的结果

Question

I have joined two SQL Queries using SQL UNION Operator

Example:

$query1 = "SELECT * FROM employees WHERE emp_first_name LIKE '%Donald%'";

$query2 = "SELECT * FROM employees WHERE emp_last_name LIKE '%George%'";

$final_query = $query1 . " UNION " . $query2

When I Run this $final_query, it shows the results of both queries if the first query's result set is not empty. If the first query has empty result set there will be no result shown even if second query has some values in the database.

Can some one explain where is the problem.

Note: Don't suggest me the use of single query, i have a reason to use two queries.

Answer 1

mysql> create table employees (emp_first_name varchar(255), emp_last_name varchar(255)); 

Query OK, 0 rows affected (0.01 sec)

mysql> insert into employees values ('hasan','khan'),('john','doe'); 

Query OK, 2 rows affected (0.00 sec) Records: 2 Duplicates: 0 Warnings: 0

mysql> select * from employees where emp_first_name like '%nothing%' union select * From employees where emp_last_name like '%doe%';

+----------------+---------------+ 
| emp_first_name | emp_last_name |
+----------------+---------------+ 
| john           | doe           |
+----------------+---------------+ 

1 row in set (0.00 sec)

Works fine for me. Either the query you posted is not the same as the one you're executing or you have problem in your code.