MySQL (optimized) query an efficiency comparison that filters a field and queries a field directly on that bar

　

Check all, 10,000 times,

$sql = "SELECT * from Mh_user where (username= ' 333 ') and (password= ' xxx ')";

Total Time 1.1420359611511

Query the username field, 10,000 times.

$sql = "Select username from Mh_user where (username= ' 333 ') and (password= ' xxx ')";
for ($i =0; $i < 10000; $i + +) {
$result = $this->db->select ($sql);
}

Total Time 0.94627690315247

Also can be seen, in apache2.4.4, MySQL 5.6.12, PHP 5.4.12, up to million times per second (table structure is simple, small capacity situation),

If the table is large, the effect may be more obvious, the first query a field

MySQL (optimized) query an efficiency comparison that filters a field and queries a field directly on that bar