没有 CTE 的分层查询

Question

由于 VistaDB 上缺少 CTEs/recursive 查询，我试图制定一个具有一定深度的可行查询来查询 PARENT/ID 分层自引用 table。我有几个想法（SQL 来自 Firebird，因为我们在服务器端使用它）：

做几个连接，像这样：

SELECT
    "A"."ID",
    "B"."ID",
    "C"."ID",
    "D"."ID"

FROM "NAVIGATION" AS A
    LEFT JOIN "NAVIGATION" AS B ON (B.PARENT = A.ID)
    LEFT JOIN "NAVIGATION" AS C ON (C.PARENT = B.ID)
    LEFT JOIN "NAVIGATION" AS D ON (D.PARENT = C.ID)

WHERE "A"."ID" = CHAR_TO_UUID('00000000-0000-0000-0000-000000000000');

然后对 A、B、C、D "ID" 列进行 COALESCE，并将其用作实际行的子查询或连接源以获取所需的内容。但是，由于第一层的第一行可能会连接到其他几行，所以这不起作用 - 我需要的是：

A       B       C      D
0       NULL    NULL   NULL
0       1       NULL   NULL
0       1       2      NULL
0       1       2      3
0       1       2      4
0       1       2      5

相反 - 正如预期的那样 - 我得到这个：

A       B       C      D
0       1       2      3
0       1       2      4
0       1       2      5

有什么方法可以获取额外的 NULL 行？

对子查询使用 UNION。但是，我想不出一个可行的语法来完成这项工作。
也许是另一种语法。我们只需要几个层次的深度。从技术上讲，我们可以在应用程序中评估 (1.) 的结果，但我更喜欢一种更优雅的方法，尽管它不必非常快。我们通常只会在客户端深入查询两三层，有时只会一层。尽管如此，最好不要按程序进行。

请求的一些示例数据：

ID    PARENT    TITLE
0     NULL      'Root Node'
1     0         '1st Level Node'
2     1         '2nd Level Node'
3     2         '3nd Level Node 1'
4     2         '3nd Level Node 2'
5     2         '3nd Level Node 3'

Answer 1

如果您有示例数据，将会有所帮助。但是，如果其他表中有匹配的行，则无法查询 return A/NULL/NULL/NULL。

获取所有层次结构的一种方法是为每个联接添加一个 NULL 值：

SELECT "A"."ID", "B"."ID", "C"."ID", "D"."ID"
FROM "NAVIGATION" AS A LEFT JOIN
     (SELECT N.PARENT, N.ID
      FROM "NAVIGATION"
      UNION ALL
      SELECT NULL, NULL
     ) B
     ON B.PARENT = A.ID
     (SELECT N.PARENT, N.ID
      FROM "NAVIGATION"
      UNION ALL
      SELECT NULL, NULL
     ) C
     ON C.PARENT = B.ID LEFT JOIN
     (SELECT N.PARENT, N.ID
      FROM "NAVIGATION"
      UNION ALL
      SELECT NULL, NULL
     ) D
     ON D.PARENT = C.ID
WHERE "A"."ID" = CHAR_TO_UUID('00000000-0000-0000-0000-000000000000');

Answer 2

这里是为好奇的人准备的完整代码。当然可以扩展到更多级别。

SELECT NAVIGATION.* FROM (

SELECT
    COALESCE("E"."ID", "D"."ID", "C"."ID", "B"."ID", "A"."ID") AS FINAL_ID

FROM "NAVIGATION" AS A LEFT JOIN
(
    SELECT NULL AS "ID", NULL AS "PARENT", NULL AS "TITLE"
    UNION ALL
    SELECT "NAVIGATION"."ID", "NAVIGATION"."PARENT", "NAVIGATION"."TITLE"
    FROM "NAVIGATION"
) AS B 
ON ("B"."PARENT" = "A"."ID") OR ("B"."ID" IS NULL) LEFT JOIN
(
    SELECT NULL AS "ID", NULL AS "PARENT", NULL AS "TITLE"
    UNION ALL
    SELECT "NAVIGATION"."ID", "NAVIGATION"."PARENT", "NAVIGATION"."TITLE"
    FROM "NAVIGATION"
) AS C
ON ("C"."PARENT" = "B"."ID") OR ("C"."ID" IS NULL) LEFT JOIN
(
    SELECT NULL AS "ID", NULL AS "PARENT", NULL AS "TITLE"
    UNION ALL
    SELECT "NAVIGATION"."ID", "NAVIGATION"."PARENT", "NAVIGATION"."TITLE"
    FROM "NAVIGATION"
) AS D
ON ("D"."PARENT" = "C"."ID") OR ("D"."ID" IS NULL) LEFT JOIN
(
    SELECT NULL AS "ID", NULL AS "PARENT", NULL AS "TITLE"
    UNION ALL
    SELECT "NAVIGATION"."ID", "NAVIGATION"."PARENT", "NAVIGATION"."TITLE"
    FROM "NAVIGATION"
) AS E
ON ("E"."PARENT" = "D"."ID") OR ("E"."ID" IS NULL)
WHERE "A"."ID" = '00000000-0000-0000-0000-000000000000'
)
LEFT JOIN NAVIGATION ON NAVIGATION.ID = FINAL_ID;

Answer 3

通常临时 tables 是 CTE 的良好替代品。事实上，有时使用临时 tables 而不是 CTE 以获得性能更好，特别是如果您计划多次加入 CTE。

运行这个

INSERT INTO #MyCTEReplacement
select ID, ParentID, 0 as Level
from Navigation
where ParentID is null

循环此操作，直到您测量到 0 个受影响的记录 - 您从 SqlCommand.ExecuteNonQuery()

获得的 return int

INSERT INTO #MyCTEReplacement
select ID, ParentID, (X.Level + 1) as Level
from Navigation N
join #MyCTEReplacement X
    on X.ID = N.ParentID
where ParentID is null

您也可以在带有循环的存储过程中执行此操作。但至少你没有使用 CURSOR (ew)，你可以为临时文件添加一个索引 table.

注意：这是上面的伪代码：不完美的 VistaDB 语法，也不完全符合您的架构需求

没有 CTE 的分层查询

Hierarchical query without CTE

sql

vistadb