Qlik 左连接到同一个表 - 它在 SQL 中如何工作？

Question

我在Qlik有这样的转变

abc:
SELECT distinct
AA.ACCOUNT_ID               AS ACCOUNT_ID_AA,
AA.ID                       AS ID_AA,
AA.F_a                      AS F_a_AA,
AA.F_b                      AS F_b_AA,
AA.F_c                      AS F_c_AA,
AA.F_d                      AS F_d_AA,
AA.F_e                      AS F_e_AA,
AA.F_f                      AS F_f_AA,
AA.F_g                      AS F_g_AA,
AA.P_A_ID                   AS P_A_ID_AA,
AA.U_P_A_ID                 AS U_P_A_ID_AA,
AA.A_C                      AS A_C_AA,
AA.R                        AS R_AA,
AA.F_h__C                   AS F_h__C_AA,
AA.I                        AS I_AA,
AA.L                        AS L_AA
FROM $(vdb).A AA
;

left join (abc)
LOAD distinct
ACCOUNT_ID_AA               AS P_ACCOUNT_ID_AA,
F_a_AA                      AS P_a_AA,
F_b_AA                      AS P_b_AA,
F_c_AA                      AS P_c_AA,
F_d_AA                      AS P_d_AA,
F_e_AA                      AS P_e_AA,
F_f_AA                      AS P_f_AA,
F_g_AA                      AS P_g_AA
Resident abc;

left join (abc)
LOAD distinct
ACCOUNT_ID_AA               AS U_P_ACCOUNT_ID_AA,
F_a_AA                      AS U_P_a_AA,
F_b_AA                      AS U_P_b_AA,
F_c_AA                      AS U_P_c_AA,
F_d_AA                      AS U_P_d_AA,
F_e_AA                      AS U_P_e_AA,
F_f_AA                      AS U_P_f_AA,
F_g_AA                      AS U_P_g_AA
Resident abc;

你能解释一下它的目的是什么吗？处理一些层次结构之间的关系？

第二个问题是qlik加入。它是如何加入的呢？有人可以向我展示这个关于 PostgreSQL 或任何其他 SQL 语言的示例吗？我唯一知道的是 Qlik 按同名的列进行连接。那么这意味着 SQL 连接将在“ON”部分中包含所有列名称？

我无法弄清楚这背后的逻辑。

Answer 1

令人困惑的部分是上面的脚本中没有“正常”连接。我所说的“正常”是指没有共同的领域可以加入。这就是在 Qlik 中创建交叉联接的方法 - 只需联接两个没有公共字段的表，Qlik 就会创建多对多关系。

如果我简化脚本并加载帐户和多一个字段：

abc:
Load * Inline [
ACCOUNT_ID_AA, F_a_AA
1            , ABC
2            , DEF
3            , GHI
];

left join (abc)

LOAD
    ACCOUNT_ID_AA as P_ACCOUNT_ID_AA,
    F_a_AA        as P_a_AA
Resident
  abc
;

left join (abc)

LOAD
    ACCOUNT_ID_AA as U_P_ACCOUNT_ID_AA,
    F_a_AA        as U_P_a_AA
Resident
  abc
;

然后当选择一个帐户ID时，结果将是：

你是对的。 Qlik 将根据公共字段自动连接表（区分大小写）。例如（伪代码）：

TableName:
Select
  AccountID,
  CustomerID
  TransactionDate
From
 Some_DB_Table
;

left join (TableName)
// TableName is optional here
// if not specified Qlik will assume
// that the table above is the one to join to

Select
  AccountID,
  CustomerID
  OrderDate
From
 Another_DB_Table
;

将等于以下 SQL：

SELECT s.AccountID       AS AccountID,
       s.CustomerID      AS CustomerID,
       s.TransactionDate AS TransactionDate,
       c.OrderDate       AS OrderDate
FROM   Some_DB_Table s
       LEFT OUTER JOIN Another_DB_Table a
                    ON s.AccountID = a.AccountID
                       AND s.CustomerID = c.CustomerID;