datawarehousing - Developer IT

Tech Article: Using Oracle GoldenGate for Real-Time Data Integration

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Learn how to install, set up, and configure Oracle GoldenGate to easily achieve seamless replication of data between Oracle Database 10g and 11g.

Tech Article: Oracle Essbase Studio Deep-Dive

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Dive into a step-by-step tutorial that reflects real-world data warehousing complexities.

Finding the maximum value/date across columns

While working on some code recently I discovered a neat little trick to find the maximum value across several columns….. So the starting point was finding the maximum date across several related tables and storing the maximum value against an aggregated record. Here's the sample setup code: USE TEMPDB IF OBJECT_ID('CUSTOMER') IS NOT NULL BEGIN DROP TABLE CUSTOMER END IF OBJECT_ID('ADDRESS') IS NOT NULL BEGIN DROP TABLE ADDRESS END IF OBJECT_ID('ORDERS') IS NOT NULL BEGIN DROP TABLE ORDERS END SELECT 1 AS CUSTOMERID, 'FREDDY KRUEGER' AS NAME, GETDATE() - 10 AS DATEUPDATED INTO CUSTOMER SELECT 100000 AS ADDRESSID, 1 AS CUSTOMERID, '1428 ELM STREET' AS ADDRESS, GETDATE() -5 AS DATEUPDATED INTO ADDRESS SELECT 123456 AS ORDERID, 1 AS CUSTOMERID, GETDATE() + 1 AS DATEUPDATED INTO ORDERS .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Now the code used a function to determine the maximum date, this performed poorly. After considering pivoting the data I opted for a case statement, this seemed reasonable until I discovered other areas which needed to determine the maximum date between 5 or more tables which didn't scale well. The final solution involved using the value clause within a sub query as followed. SELECT C.CUSTOMERID, A.ADDRESSID, (SELECT MAX(DT) FROM (Values(C.DATEUPDATED),(A.DATEUPDATED),(O.DATEUPDATED)) AS VALUE(DT)) FROM CUSTOMER C INNER JOIN ADDRESS A ON C.CUSTOMERID = A.CUSTOMERID INNER JOIN ORDERS O ON O.CUSTOMERID = C.CUSTOMERID .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } As you can see the solution scales well and can take advantage of many of the aggregate functions!

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