MySQL选择名称按字母分组，每个字母n个结果

Question

我想创建一个查询，该查询将从一个表中获取名称，然后将其与其他表合并，按字母顺序对字母的每个字母排序，然后在一个查询中将每个字母的结果限制为n个。

因此，我不会为每个字母运行26个查询，例如：

SELECT CONCAT_WS(' ',first_name,last_name) AS name FROM encyclopedia WHERE name LIKE "A%" ORDER BY rand() LIMIT 4 
SELECT CONCAT_WS(' ',first_name,last_name) AS name FROM encyclopedia WHERE name LIKE "B%" ORDER BY rand() LIMIT 4 
SELECT CONCAT_WS(' ',first_name,last_name) AS name FROM encyclopedia WHERE name LIKE "C%" ORDER BY rand() LIMIT 4

现在我有：

SELECT 
      e.id,
      CONCAT_WS(' ',first_name,last_name) AS name,
      sg.name AS sub_name, 
      sg.id AS sub_id 
      FROM ( SELECT id,first_name,last_name FROM encyclopedia ORDER BY RAND() LIMIT 4) AS e
      LEFT JOIN encyclopedia_subgenres esub
      ON ( e.id = esub.enc_id )
      LEFT JOIN subgenres sg
      ON ( esub.subgenre_id = sg.id )
      ORDER BY name

然后从PHP我从结果创建数组：

    Array
(
    [b] => Array
        (
            [2] => Array
                (
                    [name] => B Style
                    [genres] => Array
                        (
                            [26] => Classic
                            [27] => X
                            [29] => Y
                        )

                )

            [7] => Array
                (
                    [name] => Beyonce Giselle Knowles
                    [genres] => Array
                        (
                            [32] => Pop
                        )

                )

        )

    [i] => Array
        (
            [1] => Array
                (
                    [name] => Ivan D
                    [genres] => Array
                        (
                            [27] => R&B
                            [2] => Jazz
                        )

                )

        )

    [m] => Array
        (
            [3] => Array
                (
                    [name] => Maria T
                    [genres] => Array
                        (
                            [26] => Classical
                            [27] => Pop
                            [28] => Dance
                        )

                )

        )

)

但事实是，它限制了我只有4个随机结果，在同一字母或任意组合上可以是4。 有办法吗？

谢谢。

Answer 1

我认为sql不太灵活-但我不确定。 您必须为此编写存储过程。

首先创建一个生成此序列的序列：A，B，C，...，Z，A，B，C，...，Z，A，B，C，...让我们称其为magic_sequence。

然后创建一个临时表，该表具有一列init，该列是从魔术序列开始的，另一列count_down等于4。它应该有26行。 我们称它为init_table;

然后写另一个函数，acceptance_test

- take a string S with
- decrease count_down of the corresponding row in init_table
- return true if count_down > = 0; otherwise false

现在有这样的查询：

SELECT CONCAT_WS(' ',first_name,last_name) AS name FROM encyclopedia WHERE acceptance_test(name) LIMIT 4*26

如果需要，还必须随机化。