Question

I’m just trying to see if a particular user has a single resulting row of an inner join between these two tables:

create table course
(
  id int primary key auto_increment,
  name varchar(255)
);

create table persons
(
  id int primary key auto_increment,
  username varchar(255),
  courseid int,
  foreign key (courseid) references course(id)
)

Basically my query goes:

“If user SERGIO is in any course that starts with the letter SVU?” If there is any resulting row, I’d like to return true in my PHP code.

Answer 1

The following will simply return a single row with a column called found if a course starting with SVU via the LEFT() function is found for SERGIO. The DISTINCT serves to deduplicate multiple rows if the user matches multiple courses beginning with SVU.

SELECT DISTINCT 1 AS found
FROM
  persons 
  JOIN course ON persons.courseid = course.id
WHERE 
  LEFT(course.name, 3) = 'SVU'
  AND username = 'SERGIO'

Here is an example

I assume you already know how to query this in PHP and fetch the result with whatever MySQL API you are using (MySQLi, PDO, or the old mysql_*())