SQL Query Count across 2 tables - php

Question

Here is what I have (i am including only the relevant cells to each table)
table1:
- user_id
table2:
- id
- manager_id
... and I have a PHP variable
$manager_id
So, what I am trying to do is get a COUNT(*) of how many records exist in table1, but the record should only be counted if table1.user_id (which is the table2.id) has a table2.manager_id == $manager_id
So, the only way I know how to do this would be to do something like this in PHP (which is wildly inefficient):
$query = "SELECT user_id FROM table1 WHERE {my where clause}";
// execute query and place into $item[] array (not shown for brevity)
foreach ( $item as $user_id ) {
$query = "SELECT manager_id FROM table2 WHERE id = '{$user_id}';
// execute query, place each item into $row
if ( $row['manager_id'] == $manager_id ) {
// tick up count by 1
}
I am fairly certain there is a way to do this purely in SQL, but I am at a loss.

Answer 1

You could try the below query:
select count(1) from table1 t1, table2 t2 where t1.user_id = t2.id and t2.manager_id = ?

Answer 2

you need to set your where clause to have this condition i.e.
SELECT Count(user_id) FROM table1 where
table1.user_id = table2.id
AND Convert('Varchar', table2.manager_id) = $manager_id
I assume your php variable $manager_id has a string
if it is not a number then there is no need to convert the sql column (table2.manager_id) to varchar.

Answer 3

You can do this with one SELECT statement:
SELECT COUNT(*)
FROM table1
WHERE user_id IN (
SELECT id
FROM table2
WHERE manager_id = <your-value-of-manager-id>
)
In case you need to use the data and want to count on PHP side you can use the following SELECT statement using a LEFT JOIN:
SELECT table1.*
FROM table1 LEFT JOIN table2 ON table1.user_id = table2.id
WHERE table2.manager_id = <your-value-of-manager-id>
To execute the SELECT statements you should use prepared statements (using PDO or mysqli).
example using the first query:
$sql = 'SELECT COUNT(*) FROM table1 WHERE user_id IN (SELECT id FROM table2 WHERE manager_id = ?)';
$sth = $dbh->prepare($sql);
$sth->execute([$manager_id]);
$rows = $sth->fetchAll();
if (count($rows) === 1) {
echo $rows[0][0];
}
example using the second query:
$sql = 'SELECT table1.* FROM table1 LEFT JOIN table2 ON table1.user_id = table2.id WHERE table2.manager_id = ?';
$sth = $dbh->prepare($sql);
$sth->execute([$manager_id]);
$rows = $sth->fetchAll();
echo count($rows);