How to check id of one table to another table? - php

Question

How to find whether distinct value id of one table exits to another tables or not using php.
For example: Let table1 have id (not primary or unique) 4, 5, 6, 4, 6, how to check if id of table2 have 4, 5, 6 or not ?
$query_check= "select distinct(project_code) from table1";
$projects_check = mysql_query($query_check);
while ($result_check = mysql_fetch_array($projects_check)){
$all[] = $result_check[0];
}
$query = "select id from table2";
$projects = mysql_query($query);
while ($result = mysql_fetch_array($projects)){
foreach($all as $all_val){
$pro_code = $result[0];
if($pro_code != $all_val){ }
}
}

Answer 1

This SQL may help:
SELECT table2.id
FROM table2
WHERE table2.id NOT IN (
SELECT DISTINCT table1.id
FROM table1
)

Answer 2

SELECT table2.id
FROM table2
WHERE table2.id IN (
SELECT DISTINCT table1.id
FROM table1
)

Answer 3

To get a list of all the project codes from table1 that are ids in table2:-
SELECT DISTINCT table1.project_code
FROM table1
INNER JOIN table2
ON table1.project_code = table2.id
To get a list of all the project codes from table1 that are NOT ids in table2
SELECT DISTINCT table1.project_code
FROM table1
LEFT OUTER JOIN table2
ON table1.project_code = table2.id
WHERE table2.id IS NULL
If it is the entries on 2 that you want that are not on 1
SELECT DISTINCT table2.id
FROM table2
LEFT OUTER JOIN table1
ON table1.project_code = table2.id
WHERE table1.project_code IS NULL