Select into random records using mysql - mysql

Question

I have two tables in my MySql database:
Employee Table:
id | name | projectcount
---------------------------------
5 | john | 1
7 | mike | 1
8 | jane | 0
Project Table:
id | name | employeeId
---------------------------------
1 | pro1 | 5
2 | pro2 | 7
3 | pro3 | 8
CREATE TABLE EmployeeTable (
id INT,
name VARCHAR(30),
projectcount int
);
CREATE TABLE ProjectTable (
id INT,
name VARCHAR(30),
employeeId INT
);
INSERT INTO EmployeeTable (id, name, projectcount) VALUES
(5, "john", 1),
(7, "mike", 1),
(8, "jane", 0);
INSERT INTO ProjectTable (id, name, employeeId) VALUES
(1, "pro1", 5),
(2, "pro2", 7),
(3, "pro3", 8);
I would like to select 3 random records from the projects table and update the projectcount in employees table and return those records using select query.
My Approach using Stored Procedure:
DECLARE userId1 int DEFAULT 0;
DECLARE userId2 int DEFAULT 0;
DECLARE userId3 int DEFAULT 0;
DECLARE projectId1 int DEFAULT 0;
DECLARE projectId2 int DEFAULT 0;
DECLARE projectId3 int DEFAULT 0;
select id, employeeid into projectId1, userId1 from project order by RAND() LIMIT 1;
select id, employeeid into projectId2, userId2 from project order by RAND() LIMIT 1;
select id, employeeid into projectId3, userId3 from project order by RAND() LIMIT 1;
update employee set projectcount = projectcount + 1 where id = userId1;
update employee set projectcount = projectcount + 1 where id = userId2;
update employee set projectcount = projectcount + 1 where id = userId3;
select * from project where id in (projectId1, projectId2, projectId3);
The above code works but written in more static way. Is there any improvements done to this to look more cleaner. Thanks.

Answer 1

PLan A
"Is there any improvements done to this to look more cleaner." Do only one request at a time.
Since that probably does not satisfy your intended meaning of "cleaner", I will continue:
Plan B
Flip things around. And use a transaction.
This runs 3 times as fast, and fixes one potential bug. Does that qualify as "cleaner"?
BEGIN;
SELECT #ids := GROUP_CONCAT(id)
-- I assume that `id` is the PRIMARY KEY of `project`?
from project
order by RAND() LIMIT 3;
-- That will run 3 times as fast as 3 separate SELECTs.
-- It avoids tallying the same id 3 times
-- but it may hit the same employee 3 times
SET #sql = CONCAT("UPDATE employee
SET projectcount = projectcount + 1
WHERE id IN (", #ids, ")");
PREPARE _sql FROM #sql;
EXECUTE _sql;
DEALLOCATE PREPARE _sql;
... -- similar execute to get the `SELECT *`
COMMIT;
If you have millions of rows you are picking from, then be aware that ORDER BY RAND() always requires a full table scan and a sort. Here are some kludges to speed that up: http://mysql.rjweb.org/doc.php/random
Plan C
Tighten up the specs (no dup projects, double-assigning a user, define "cleaner", etc) Then we can look for other ways.