Question

由于VistaDB上缺少CTE /递归查询，我试图用一定深度制定一个可行的查询来查询PARENT / ID分层自引用表。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COALESCE在A，B，C，D＆＃34; ID＆＃34;列，并将其用作实际行的子查询或联接源以获取所需内容。但是，由于第一级的第一行可能会连接到其他几行，但这并不起作用 - 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 - 我得到了这个：

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

获取额外NULL行的任何方式？

将UNION与子查询一起使用。但是，我无法找到一种可行的语法来完成这项任务。
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，但我更喜欢更优雅的方法，尽管它不必非常快。我们通常只在客户端上查询两到三个级别，有时只有一个级别。不过，在程序上不做这件事会很好。

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

如果您有样本数据会有所帮助。但是，如果其他表中存在匹配的行，则查询无法返回A / NULL / NULL / NULL。

获取所有层次结构的一种方法是为每个连接添加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

以下是好奇的完整代码。它可以扩展到更多层次。

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

通常临时表是CTE的良好替代品。实际上，有时最好使用临时表而不是CTE来提高性能，尤其是如果您计划多次加入CTE时。

运行此

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

循环这个，直到你测量0个受影响的记录 - 你从SqlCommand.ExecuteNonQuery（）获得的返回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），你可以在临时表中添加一个索引。

注意：这是上面的伪代码：不完美的VistaDB语法，并不完全匹配您的架构需求

没有CTE

3 个答案: