多次查询数据库如何更有效率

$arr = [];
$go= $dbh -> query("select id,gid from table1");while($rs = $go -> fetch(PDO :: FETCH_ASSOC)){$arr['table1'] = $rs;}
$go= $dbh -> query("select id,gid from table2");while($rs = $go -> fetch(PDO :: FETCH_ASSOC)){$arr['table2'] = $rs;}
$go= $dbh -> query("select id,gid from table3");while($rs = $go -> fetch(PDO :: FETCH_ASSOC)){$arr['table3'] = $rs;}
$go= $dbh -> query("select id,gid from table4");while($rs = $go -> fetch(PDO :: FETCH_ASSOC)){$arr['table4'] = $rs;}
....
如上，是否只能一个一个的查询再存储到数据中？是否每执行一个SQL语句就访问一次数据库？如何更有效率的处理查询语句结果到数组中？