Alternative to Intersect in MySQL

Question

I need to implement the following query in MySQL.

(select * from emovis_reporting where (id=3 and cut_name= '全プロセス' and cut_name='恐慌') )  intersect ( select * from emovis_reporting where (id=3) and ( cut_name='全プロセス' or cut_name='恐慌') ) 

I know that intersect is not in MySQL. So I need another way. Please guide me.

Answer 1

Microsoft SQL Server's INTERSECT "returns any distinct values that are returned by both the query on the left and right sides of the INTERSECT operand" This is different from a standard INNER JOIN or WHERE EXISTS query.

SQL Server

CREATE TABLE table_a (     id INT PRIMARY KEY,     value VARCHAR(255) );  CREATE TABLE table_b (     id INT PRIMARY KEY,     value VARCHAR(255) );  INSERT INTO table_a VALUES (1, 'A'), (2, 'B'), (3, 'B'); INSERT INTO table_b VALUES (1, 'B');  SELECT value FROM table_a INTERSECT SELECT value FROM table_b  value ----- B  (1 rows affected) 

MySQL

CREATE TABLE `table_a` (   `id` INT NOT NULL AUTO_INCREMENT,   `value` varchar(255),   PRIMARY KEY (`id`) ) ENGINE=InnoDB;  CREATE TABLE `table_b` LIKE `table_a`;  INSERT INTO table_a VALUES (1, 'A'), (2, 'B'), (3, 'B'); INSERT INTO table_b VALUES (1, 'B');  SELECT value FROM table_a INNER JOIN table_b USING (value);  +-------+ | value | +-------+ | B     | | B     | +-------+ 2 rows in set (0.00 sec)  SELECT value FROM table_a WHERE (value) IN (SELECT value FROM table_b);  +-------+ | value | +-------+ | B     | | B     | +-------+ 

With this particular question, the id column is involved, so duplicate values will not be returned, but for the sake of completeness, here's a MySQL alternative using INNER JOIN and DISTINCT:

SELECT DISTINCT value FROM table_a INNER JOIN table_b USING (value);  +-------+ | value | +-------+ | B     | +-------+ 

And another example using WHERE ... IN and DISTINCT:

SELECT DISTINCT value FROM table_a WHERE (value) IN (SELECT value FROM table_b);  +-------+ | value | +-------+ | B     | +-------+ 

Answer 2

There is a more effective way of generating an intersect, by using UNION ALL and GROUP BY. Performances are twice better according to my tests on large datasets.

Example:

SELECT t1.value from (   (SELECT DISTINCT value FROM table_a)   UNION ALL    (SELECT DISTINCT value FROM table_b) ) AS t1 GROUP BY value HAVING count(*) >= 2; 

It is more effective, because with the INNER JOIN solution, MySQL will look up for the results of the first query, then for each row, look up for the result in the second query. With the UNION ALL-GROUP BY solution, it will query results of the first query, results of the second query, then group the results all together at once.