Question

我在 SQL Server 中有一个SQL查询，就像这样

SELECT 
    CASE WHEN ROW_NUMBER() OVER(PARTITION BY _no ORDER BY _no asc) = 1 THEN 
                        _no ELSE '' END 
    as row_no,
    _no,
    _name,
    r._names
FROM
(
    SELECT '1' as _no, 'vikas' as _name UNION ALL
    SELECT '1', 'kratika' UNION ALL
    SELECT '2', 'vikas' UNION ALL
    SELECT '1', 'kratika kastwar' 
) t
INNER JOIN 
(
    SELECT '1' as _nos, 'One' as _names UNION ALL
    SELECT '2', 'two' 
) r
ON r._nos = t._no
ORDER BY _no

输出：

row_no _no  _name           _names
------ ---- --------------- ------
1      1    kratika         One
       1    kratika kastwar One
       1    vikas           One
2      2    vikas           two

我在 MySQL 这样做

SELECT 
    CASE WHEN _no = @i THEN '' ELSE @i := _no END
    as row_no,
    _no,
    _name,
    r._names
FROM
(
    SELECT '1' as _no, 'vikas' as _name UNION ALL
    SELECT '1', 'kratika' UNION ALL
    SELECT '2', 'vikas' UNION ALL
    SELECT '1', 'kratika kastwar' 
) t
INNER JOIN 
(
    SELECT '1' as _nos, 'One' as _names UNION ALL
    SELECT '2', 'two' 
) r
ON r._nos = t._no
,
(SELECT @i := '') temp
ORDER BY _no

输出：

1   1   vikas           One
    1   kratika         One
1   1   kratika kastwar One
2   2   vikas           two

但我希望 MySQL 中的输出像这样

1      1    kratika         One
       1    kratika kastwar One
       1    vikas           One
2      2    vikas           two

我不想在 MySQL 中使用这样的查询作为desc here MYSQL Order By W/Count

SELECT 
    CASE WHEN _no = @i THEN '' ELSE @i := _no END
    as row_no,
    _no,
    _name,
    _names
FROM
(SELECT 
    *
FROM
(
    SELECT '1' as _no, 'vikas' as _name UNION ALL
    SELECT '1', 'kratika' UNION ALL
    SELECT '2', 'vikas' UNION ALL
    SELECT '1', 'kratika kastwar' 
) t
INNER JOIN 
(
    SELECT '1' as _nos, 'One' as _names UNION ALL
    SELECT '2', 'two' 
) r
ON r._nos = t._no
,
(SELECT @i := '') temp
ORDER BY _no) t

如何在MySQL中实现相同，查询性能是主要参数

Answer 1

我认为这里发生的事情是MySQL正在构造结果集，然后经过一个额外的步骤来根据ORDER BY子句对它进行排序。由于'kratika kastwar'行位于_no为2的行之后，因此您会收到意外的输出。

我想，解决方案是将基本的SELECT（没有特殊的用户变量shenanigans）放在FROM子句的子查询中，并应用ORDER BY子句子查询。然后在外部查询中执行用户变量工作。这样排序已经发生了。

编辑：我看到你说你不想这样做。我认为你没有选择，除非你能找到一种方法让MySQL不通过对计算结果执行文件排序步骤来执行ORDER BY（非常不可能）。

Answer 2

SELECT 
    CASE WHEN _no = @i THEN '' ELSE @i := _no END
    as row_no,
    _no,
    _name,
    _names
FROM
(SELECT 
    *
FROM
(
    SELECT '1' as _no, 'vikas' as _name UNION ALL
    SELECT '1', 'kratika' UNION ALL
    SELECT '2', 'vikas' UNION ALL
    SELECT '1', 'kratika kastwar' 
) t
INNER JOIN 
(
    SELECT '1' as _nos, 'One' as _names UNION ALL
    SELECT '2', 'two' 
) r
ON r._nos = t._no
,
(SELECT @i := '')

MySQL与SQL Server的问题排序

2 个答案: