Get result of mysql_query inside while of mysql_fetch_array - php

Question

I am using a code something like below to get data from the second table by matching the id of first table. Code is working well, but I know it slow down the performance, I am a new bee. Please help me to do the same by an easy and correct way.
<?php
$result1 = mysql_query("SELECT * FROM table1 ") or die(mysql_error());
while($row1 = mysql_fetch_array( $result1 ))
{
$tab1_id = $row1['tab1_id'];
echo $row['tab1_col1'] . "-";
$result2 = mysql_query("SELECT * FROM table2 WHERE tab2_col1='$tab1_id' ") or die(mysql_error());
while( $row2 = mysql_fetch_array( $result2 ))
{
echo $row2['tab2_col2'] . "-";
echo $row2['tab2_col3'] . "</br>";
}
}
?>

Answer 1

You can join the two tables and process the result in a single loop. You will need some extra logic to check if the id of table1 changes, because you'll only want to output this value when there's a different id:
<?php
// Join the tables and make sure to order by the id of table1.
$result1 = mysql_query("
SELECT
*
FROM
table1 t1
LEFT JOIN table2 t2 ON t2.col1 = t1.id
ORDER BY
t1.id") or die(mysql_error());
// A variable to remember the previous id on each iteration.
$previous_tab1_id = null;
while($row = mysql_fetch_array( $result1 ))
{
$tab1_id = $row['tab1_id'];
// Only output the 'header' if there is a different id for table1.
if ($tab1_id !== $previous_tab1_id)
{
$previous_tab1_id = $tab1_id;
echo $row['tab1_col1'] . "-";
}
// Only output details if there are details. There will still be a record
// for table1 if there are no details in table2, because of the LEFT JOIN
// If you don't want that, you can use INNER JOIN instead, and you won't need
// the 'if' below.
if ($row['tab2_col1'] !== null) {
echo $row['tab2_col2'] . "-";
echo $row['tab2_col3'] . "</br>";
}
}

Answer 2

Instead of having 2 while loops, what you can do is join the 2 tables and then iterate over the result.
If you're not sure what join is look here: https://dev.mysql.com/doc/refman/5.1/de/join.html
Also here is a fairly simple query written using join: Join Query Example

Answer 3

You can use this. One relation with two tables:
<?php
$result1 = mysql_query("SELECT tab2_col2, tab2_col3 FROM table1, table2 where tab2_col1 = tab1_id ") or die(mysql_error());
while($row1 = mysql_fetch_array( $result1 ),)
{
echo $row2['tab2_col2'] . "-";
echo $row2['tab2_col3'] . "</br>";
}
?>

Answer 4

Like Sushant said, it would be better to use one JOIN or simpler something like that:
SELECT * FROM table1, table2 WHERE `table1`.`id` = `table2`.`id