问题描述
使用以下 MySQL 表:
With the following MySQL table:
+-----------------------------+
+ id INT UNSIGNED +
+ name VARCHAR(100) +
+-----------------------------+
当按name ASC 排序时，如何选择单个 行及其在表中其他行中的位置.所以如果表数据是这样的，按名称排序时:
How can I select a single row AND its position amongst the other rows in the table, when sorted by name ASC. So if the table data looks like this, when sorted by name:
+-----------------------------+
+ id | name +
+-----------------------------+
+ 5 | Alpha +
+ 7 | Beta +
+ 3 | Delta +
+ ..... +
+ 1 | Zed +
+-----------------------------+
如何选择 Beta 行以获得该行的当前位置?我正在寻找的结果集是这样的:
How could I select the Beta row getting the current position of that row? The result set I'm looking for would be something like this:
+-----------------------------+
+ id | position | name +
+-----------------------------+
+ 7 | 2 | Beta +
+-----------------------------+
我可以做一个简单的 SELECT * FROM tbl ORDER BY name ASC 然后枚举 PHP 中的行，但是只为一行加载一个可能很大的结果集似乎很浪费.
I can do a simple SELECT * FROM tbl ORDER BY name ASC then enumerate the rows in PHP, but it seems wasteful to load a potentially large resultset just for a single row.
推荐答案
使用这个:
SELECT x.id,
x.position,
x.name
FROM (SELECT t.id,
t.name,
@rownum := @rownum + 1 AS position
FROM TABLE t
JOIN (SELECT @rownum := 0) r
ORDER BY t.name) x
WHERE x.name = 'Beta'
...获取唯一的位置值.这个:
...to get a unique position value. This:
SELECT t.id,
(SELECT COUNT(*)
FROM TABLE x
WHERE x.name <= t.name) AS position,
t.name
FROM TABLE t
WHERE t.name = 'Beta'
...会给关系相同的值.IE:如果第二个位置有两个值，当第一个查询将位置 2 分配给其中一个，将 3 分配给另一个时，它们的位置都会为 2...
...will give ties the same value. IE: If there are two values at second place, they'll both have a position of 2 when the first query will give a position of 2 to one of them, and 3 to the other...
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