标签: cross-join

目前,我无法使用典型的数据库,因此暂时使用excel.有任何想法吗？

该

今天,在使用sql server进行10年开发的第一次中,我在生产查询中使用了交叉连接.我需要将结果集填充到报表中,并发现具有creative where子句的两个表之间的交叉连接是一个很好的解决方案.我想知道在交叉连接的生产代码中有什么用处？

更新:托尼安德鲁斯发布的代码非常接近我使用交叉联接的代码.相信我,我理解使用交叉连接的含义,并不会轻易做到这一点.我很高兴最终使用它(我是一个书呆子) - 有点像我第一次使用完全外连接的时候.

感谢大家的答案!这是我使用交叉连接的方式:

SELECT  CLASS, [Trans-Date] as Trans_Date,
SUM(CASE TRANS
     WHEN 'SCR' THEN [Std-Labor-Value]
     WHEN 'S+' THEN [Std-Labor-Value]
     WHEN 'S-' THEN [Std-Labor-Value]
     WHEN 'SAL' THEN [Std-Labor-Value]
     WHEN 'OUT' THEN [Std-Labor-Value]
     ELSE 0
END) AS [LABOR SCRAP],
SUM(CASE TRANS
     WHEN 'SCR' THEN  [Std-Material-Value]
     WHEN 'S+' THEN [Std-Material-Value]
     WHEN 'S-' THEN  [Std-Material-Value]
     WHEN 'SAL' THEN [Std-Material-Value]
     ELSE 0
END) AS [MATERIAL SCRAP], 
SUM(CASE TRANS WHEN 'RWK' THEN [Act-Labor-Value] ELSE 0 END) AS [LABOR REWORK],
SUM(CASE TRANS 
     WHEN 'PRD' …

Baur&King在他们的书中说:

隐式连接始终沿着多对一或一对一关联,而不是通过集合值关联.

[P 646,Ch 14]

但是当我在代码中执行此操作时,它会生成CROSS JOIN而不是INNER JOIN.

映射来自Member2(多对一) - > CLub.

但Club2没有关于会员的信息,并且Member2拥有Club2的外键.

我的疑问是

// Implicit: Find all UK club member who is female
Transaction t1 = HibernateUtil.begin();
Query query =
    HibernateUtil.getSession().createQuery("From Member2 m where m.club2.country = 'UK' ");
List<Member2> memList = query.list();
for (Member2 m : memList)
  System.out.println(m);
HibernateUtil.end(t1);

并且,Hibernate生成以下SQL查询:

Hibernate: 
    select
        member2x0_.member_id as member_i1_1_,
        member2x0_.club_id as club_id5_1_,
        member2x0_.member_age as member_a2_1_,
        member2x0_.member_name as member_n3_1_,
        member2x0_.member_sex as member_s4_1_ 
    from
        TBL_MEMBER2 member2x0_ cross 
    join …

如果有这样的数据:

A = LOAD 'data' AS (a1:int,a2:int,a3:int);

DUMP A;
(1,2,3)
(4,2,1)

然后在A,A上完成交叉连接:

B = CROSS A, A;

DUMP B;
(1,2,3)
(4,2,1)

为什么第二个A从查询中优化出来？

信息:猪版0.11

==更新==

如果我按A排序:

C = ORDER A BY a1;
D = CROSS A, C;

它将提供正确的交叉连接.

我遇到Hibernate生成无效SQL的问题.具体来说,混合和匹配隐式和显式连接.这似乎是一个开放的bug.

但是,我不确定为什么这是无效的SQL.我想出了一个生成相同语法异常的小玩具示例.

架构

CREATE TABLE Employee (
    employeeID INT,
    name VARCHAR(255),
    managerEmployeeID INT   
)

数据

INSERT INTO Employee (employeeID, name) VALUES (1, 'Gary')
INSERT INTO Employee (employeeID, name, managerEmployeeID) VALUES (2, 'Bob', 1)

工作SQL

这两个查询都有效.我意识到有笛卡尔积; 那是故意的.

明确的加入:

SELECT e1.name,
       e2.name,
       e1Manager.name
  FROM Employee e1
 CROSS JOIN Employee e2
 INNER JOIN Employee e1Manager
    ON e1.managerEmployeeID = e1Manager.employeeID

隐含的JOIN:

SELECT e1.name,
       e2.name,
       e1Manager.name
  FROM Employee e1,
       Employee e2,
       Employee e1Manager
 WHERE e1.managerEmployeeID = e1Manager.employeeID

无效的SQL

此查询不适用于MSSQL 2000/2008或MySQL:

SELECT …

我正在尝试进行交叉连接（来自此处的原始问题），并且我有 500GB 的内存。问题是最后的data.table行数超过 2^31 行，所以我收到此错误：

Error in vecseq(f__, len__, if (allow.cartesian || notjoin || !anyDuplicated(f__,  : 
  Join results in more than 2^31 rows (internal vecseq reached physical limit). Very likely misspecified join. Check for duplicate key values in i each of which join to the same group in x over and over again. If that's ok, try by=.EACHI to run j for each group to avoid the large allocation. Otherwise, please search for this error message …

我一直试图通过我的查询来追踪问题.查询实际上是由HQL从HQL生成的,但生成的SQL没有达到我的预期.稍微修改SQL会产生正确的结果,但我不确定为什么修改应该有所不同.

原始查询(不返回任何行)

select sched.id, max(txn.dttm), acc.id
from PaymentSchedulePeriod sched 
cross join PaymentSchedulePayment pay
right outer join AccountTransaction txn on pay.accountTransactionFk=txn.id 
right outer join Account acc on txn.accountFk=acc.id 
where sched.accountFk=acc.id 
group by sched.id, acc.id

修改后的查询 - 用逗号替换交叉连接(隐式交叉连接)

返回一行

select sched.id, max(txn.dttm), acc.id
from PaymentSchedulePeriod sched 
,PaymentSchedulePayment pay
right outer join AccountTransaction txn on pay.accountTransactionFk=txn.id 
right outer join Account acc on txn.accountFk=acc.id 
where sched.accountFk=acc.id 
group by sched.id, acc.id

我的理解可能是不正确的,写作from Table1 a, Table2 b与写作是一样的from Table 1 a cross join Table2 …

有什么区别:

select t1.a1, t1.a2, t1.a3 from t1 cross join t2 where t1.a3 = t2.a1

和:

select t1.a1, t1.a2, t1.a3 from t1,t2 where t1.a3=t2.a1;

我可以互换使用吗？

我有一个data.table对象,其中包含多个指定唯一案例的列.在下面的小示例中,变量" name"," job"和" sex"指定唯一ID.我想添加缺失的行,以便每个case都有一行用于另一个变量的每个可能实例," from"(类似于expand.grid).

library(data.table)
set.seed(1)
mydata <- data.table(name = c("john","john","john","john","mary","chris","chris","chris"),
                 job = c("teacher","teacher","teacher","teacher","police","lawyer","lawyer","doctor"),
                 sex = c("male","male","male","male","female","female","male","male"),
                 from = c("NYT","USAT","BG","TIME","USAT","BG","NYT","NYT"),
                 score = rnorm(8))

setkeyv(mydata, cols=c("name","job","sex"))

mydata[CJ(unique(name, job, sex), unique(from))]

这是当前的data.table对象:

> mydata
    name     job    sex from      score
1:  john teacher   male  NYT -0.6264538
2:  john teacher   male USAT  0.1836433
3:  john teacher   male   BG -0.8356286
4:  john teacher   male TIME  1.5952808
5:  mary  police female USAT  0.3295078
6: chris  lawyer female …

简介:我见过的MDX连接的大多数示例都涉及加入相对较小的集合,例如每个集合数十或数百个项目.但我发现自己也想尝试加入(特别是"非空加入")集合,每个集合包含数千或数万个项目,到目前为止它还不能正常运行.我想知道这是否可以使用,或者我是否需要考虑使用除Mondrian/OLAP之外的其他东西.

具体来说,我有一个记录公司(n = 7000)和客户(n = 27000)之间互动的立方体.目前公司和客户都是完全扁平化的层次结构; 有所有级别和个人 - 公司级别,其间没有其他级别.有一个中央事实表,以及公司和客户的单独维度表.

我的用户至少似乎想要沿着这些方向获取摘要报告,聚合公司和客户之间的所有非空交互:

select
  [Measures].[Amount] on columns,
  NonEmptyCrossJoin([Firm].Children,
                      [Client].Children) on rows
from MyCube

但是这个查询及其变体在我的测试Mondrian设置中不起作用.要么我得到一个OutOfMemoryException(在2GB的Java堆上),要么Java似乎花了不可思议的长时间在mondrian.rolap.RolapResult $ AxisMember.mergeTuple(TupleCursor).(如果有帮助的话,我可以提供更完整的堆栈跟踪.)"不可思议的长"我的意思是Java在我放弃之前会在数小时内停留在查询中.

我最初的预期上面的查询进行确定,因为从概念上讲它可以做一定程度的只是在做沿着这些路线的SQL查询有效:

select Firm, Client, Sum(Amount) as n
from fact, firm, client
where fact.firmid = firm.firmid and fact.clientid = client.clientid
group by Firm, Client

(事实上​​,如果我直接在MySql中执行这样的操作,则执行时间不会超过15秒.)

但是从调试日志来看,Mondrian似乎没有尝试这种优化.相反,它似乎是在内部进行连接,并且最终变得特别慢.我在我的mondrian.properties中设置了mondrian.native.crossjoin.enable = true,但这似乎不是Mondrian能够"生成本机"的连接类型之一.(如果我打开mondrian.native.unsupported.alert = ERROR,那么我得到相应的异常.)

我想知道我是否需要阻止我的用户尝试加入如此大的尺寸/集合,或者Mondrian是否可能不是我在这里寻找的工具.但也许我只是做错了什么.