4.8 外存维表
SQL
SELECT Customers.CustomerID,CustomerName,Region,City,Amount
FROM Customers
INNER JOIN Orders ON Orders.CustomerID=Customers.CustomerID
WHERE OrderDate<='2021-12-31' and OrderDate>='2021-01-01'
ORDER BY Amount DESC
LIMIT 1,100
SPL
| A | |
|---|---|
| 1 | >st=date(“2021-01-01”), et=date(“2021-12-31”), start=days@o(st), end=days@o(et) |
| 2 | =file(“Orders_Time.ctx”).open().cursor@x(Amount,CustomerID;OrderDate>=start && OrderDate<=end) |
| 3 | =A2.groups(;top(100;-Amount)).#1 |
| 4 | =A3.joinx@q(CustomerID,file(“Customers.ctx”).open():CustomerID,CustomerName,Region,City) |
A4 当事实表的数据较少，可以全内存放下，且维表特别大的时候，采用 joinx@q 函数，可快速定位并关联维表，不必对维表全遍历，从而提升效率
