Question

I’m looking to count the amount of fields in 5 tables and display a result. I currently do this for a single table

    $variable = mysql_num_rows(mysql_query("SELECT id FROM table1"));

What is the most efficient way to include and count all id from table2, table3, table4 and table5?

Thanks

Answer 1

Use UNION ALL to combine the SELECT queries on all the tables to get the total number of IDs from all the tables. Use UNION instead to get total number of distinct IDs from all the tables.

$variable = mysql_num_rows(mysql_query("
    "SELECT id FROM table1 " .
    "UNION ALL " .
    "SELECT id FROM table2 " .
    "UNION ALL " .
    "SELECT id FROM table3 " .
    "UNION ALL " .
    "SELECT id FROM table4 " .
    "UNION ALL " .
    "SELECT id FROM table5"));