mysql_num_rows和condition

Question

大家好，我正在尝试使用更有效的方法，而不是从多个查询中使用mysql_num_rows。我是否可以使用一个查询，例如，根据condition if $type=="a"计算mysql_num_rows()？并为每个..声明变量用于b行，c行，d行等。谢谢

$rows_a = mysql_query("SELECT $type FROM table WHERE $type = 'a'");
$a_rows = mysql_num_rows($rows_a);

$rows_b = mysql_query("SELECT $type FROM table WHERE $type = 'b'");
$b_rows = mysql_num_rows($rows_b);

$rows_c = mysql_query("SELECT $type FROM table WHERE $type = 'c'");
$c_rows = mysql_num_rows($rows_c);

$rows_d = mysql_query("SELECT $type FROM table WHERE $type = 'd'");
$d_rows = mysql_num_rows($rows_d);

Answer 1

SELECT COUNT(id), type FROM table GROUP BY type

Answer 2

可能如下所示：(如果没有主ID列)

SELECT COUNT(*) as num_rows, type FROM table WHERE type IN ('a', 'b', 'c', 'd') GROUP BY type 

或者是动态的：

SELECT COUNT(*) as num_rows, type FROM table WHERE type IN ('select types from a sub query') GROUP BY type