php mysql while loop query optimization - php

Question

I have php/mysql script running which is like this:
$sql = "select a.column1 from table1 a";
$query = mysql_query($sql);
while ($fec = mysql_fetch_assoc($query)) {
$sub1 = "select column1,column2 from subtable1 where id=" . $fec['a.column1'];
$subquery1 = mysql_query($sub1);
while ($subfec1 = mysql_fetch_assoc($subquery1)) {
//all data .....
}
$sub1 = "select column1,column2 from subtable2 where id=" . $fec['a.column1'];
$subquery2 = mysql_query($sub2);
while ($subfec2 = mysql_fetch_assoc($subquery2)) {
//all data .....
}
$sub2 = "select column1,column2 from subtable3 where id=" . $fec['a.column1'];
$subquery3 = mysql_query($sub3);
while ($subfec3 = mysql_fetch_assoc($subquery3)) {
//all data .....
}
}
Now I've many many many records in table1, subtable1, subtable2 and subtable3. And problem is that it takes around 7 hours to display the results. Moreover the CPU Usage is 100%
Please suggest the optimization tips to overcome this issue.

Answer 1

Use a single query to get all records
SELECT
a.column1,
s.column1,
s.column2,
s2.column1,
s2.column2,
s3.column1,
s3.column2
FROM table1 a
LEFT JOIN subtable1 s ON s.id = a.column1
LEFT JOIN subtable2 s2 ON s.id = a.column1
LEFT JOIN subtable3 s3 ON s.id = a.column1
Here
$sql="
SELECT
a.column1 acolumn1,
s.column1 scolumn1,
s.column2 scolumn2,
s2.column1 s2column1,
s2.column2 s2column2,
s3.column1 s3column1,
s3.column2 s3column2
FROM table1 a
LEFT JOIN subtable1 s ON s.id = a.column1
LEFT JOIN subtable2 s2 ON s.id = a.column1
LEFT JOIN subtable3 s3 ON s.id = a.column1";
$query=mysql_query($sql);
while ($fec=mysql_fetch_assoc($query)) {
// display any info here
}
Use aliases for accessing different table columns