Question

我正在计算5个表中的字段数量并显示结果。我目前为单个表

执行此操作

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

从id，table2，table3和table4中包含和统计所有table5的最有效方法是什么？

由于

Answer 1

使用UNION ALL组合所有表的SELECT查询，以获取所有表中的ID总数。请使用UNION来获取所有表格中distinct个ID的总数。

$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"));

Answer 2

不要从数据库中获取所有行，只需获取ID数。让MySQL算起来而不是PHP。

    $variable1 = mysql_query("SELECT COUNT(id) FROM table1");
    $variable2 = mysql_query("SELECT COUNT(id) FROM table2");
    $variable3 = mysql_query("SELECT COUNT(id) FROM table3");
    $variable4 = mysql_query("SELECT COUNT(id) FROM table4");
    $variable5 = mysql_query("SELECT COUNT(id) FROM table5");

    $variable = $variable1 + $variable2 + $variable3 + $variable4 +$variable5;

不要做UNION或JOIN，如果你只是需要计算，这是一项重量级的工作。

Answer 3

SELECT count(t1.id)+count(t2.id)+count(t3.id)+count(t4.id)+count(t5.id) from table1 as t1, table2 as t2, table3 as t3, table4 as t4, table5 as t5

Answer 4

SELECT COUNT(id) FROM table2

等

Answer 5

尝试这样的联合语法：

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

结束，祝你好运

Answer 6

第一种方法：

$query = mysql_query("
    select * from(
        SELECT id FROM table1
        union
        SELECT id FROM table2
        union
        SELECT id FROM table3
        union
        SELECT id FROM table4
    )
");
while ($row = mysql_fetch_assoc($query)) {
    //some operations
}
$variable = mysql_num_rows($query);

第二种方法：

$query = mysql_query("
    select count(*) cnt from(
        SELECT id FROM table1
        union
        SELECT id FROM table2
        union
        SELECT id FROM table3
        union
        SELECT id FROM table4
    )
");

while ($row = mysql_fetch_assoc($query)) {
    $variable = $query['cnt'];
}

来自多个表的mysql_num_rows

6 个答案: