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GREATEST() and LEAST() functions in Azure SQL Database

Antonios Chatzipavlis

Μια απαίτηση αρκετών χρόνων υλοποιήθηκε μερικώς στον SQL Server καθώς αυτή την στιγμή είναι μόνο διαθέσιμη στις Azure SQL Databases και αφορά δύο T-SQL functions που υπάρχουν σε άλλα RDBMS εδώ και χρόνια.

Η απαίτηση αυτή αφορά τις GEATEST και LEAST functions.

Η πρώτη επιστρέφει την μεγαλύτερη τιμή από τις τιμές που εισάγονται στις παραμέτρους της και δεύτερη την μικρότερη τιμή.

Ακόμα το documentation δεν είναι ενημερωμένο με αυτές αλλά η σύνταξη τους είναι αρκετά απλή.

Syntax

SELECT GREATEST(<value1>,<value2>…<valueN>);
SELECT LEAST(<value1>,<value2>…<valueN>);

Η προσθήκη αυτή κάνει αρκετά καλύτερη την συγγραφή των queries καθώς στο παρελθόν (αλλά ακόμα και τώρα όσον αφορά τον SQL Server) έπρεπε να καταφύγουμε σε διάφορες τεχνικές όπως αυτή που παρουσιάζω στο παράδειγμα παρακάτω με την χρήση του APPLY operator

Mimic GREATEST and LEAST function

select    
    o.orderid, 
    o.orderdate,
    o.requireddate,
    o.shippeddate,
    min(dd.dates) as min_date,
    max(dd.dates) as max_date
from 
    sales.Orders as o
outer apply 
    ( values (o.orderdate), (o.requireddate), (o.shippeddate) ) as dd(dates)
group by 
    o.orderid,
    o.orderdate, 
    o.requireddate,
    o.shippeddate;

Αντί για αυτό πλέον (ακόμα μόνο σε Azure SQL Databases) το παραπάνω query γίνεται όπως παρακάτω.

GREATEST and LEAST function usage

select    
    o.orderid, 
    o.orderdate,
    o.requireddate,
    o.shippeddate,
    LEAST(o.orderdate, o.requireddate, o.shippeddate) as min_date,
    GREATEST(o.orderdate, o.requireddate, o.shippeddate) as max_date
from 
    sales.Orders as o;

Θεωρώ ότι σύντομα θα είναι διαθέσιμες και στο SQL Server.


//Antonios Chatzipavlis


Antonios Chatzipavlis

Antonios Chatzipavlis

Antonios is a Data Solutions Consultant and Trainer. He has been working in IT since 1988. In his career, he has worked as senior developer, IT Manager, Solutions Architect and IT Consultant. Since 1995 he has been devoted on new technologies and software development tools, mainly by Microsoft, either by training company staff and colleagues or assisting them in design, development and implementation as a consultant or chief developer. He has focused in Databases and Data Science since 1995. He specialized in Microsoft SQL Server since version 6.0 in areas like SQL Server Internals, Database Design and Development, Business Intelligence and in 2010 he has started working with Azure Data Platform, NoSQL databases, Big Data Technologies and Machine Learning. He is an active member of many IT communities in Greece, answering colleagues' questions and writing articles in his web site. He is the owner of SQLschool.gr which is a community portal with a lot of information about Microsoft SQL Server. He has been a Microsoft Certified Trainer (MCT) since 2000. Microsoft honored him as MVP on Data Platform due to his activities in SQL Server since 2010. He holds a large number of Microsoft Certifications and Microsoft SQL Server Certifications since version 6.5.



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