I want to select the first row of each group grouped by the PostgreSQL keyword GROUP BY. Suppose I am working on purchase reporting and I want to select the customer who has a max value of the price.
I have the following table
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Result: ![]()
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I have the following table
CREATETABLEorders ( idserialnotnull, nametext, itemQtyinteger, pricedecimal ); --Insert some records insertintoorders(name,itemqty,price) values('Ashish',2,200); insertintoorders(name,itemqty,price) values('Naina',8,300); insertintoorders(name,itemqty,price) values('Mamta',10,2000); insertintoorders(name,itemqty,price) values('Ashish',4,500); insertintoorders(name,itemqty,price) values('Naina',4,100); insertintoorders(name,itemqty,price) values('Mamta',6,2500); insertintoorders(name,itemqty,price) values('Mamta',5,1500); |
Simple select query
SELECT*FROMorders
Result:
But I want to result as below:
There are several ways to resolve this problem, please the below PostgreSQL statements/t-sql queries.
1- Using common table expression:
WITHcteAS ( SELECTp.id, p.name, p.itemqty, p.price, ROW_NUMBER()OVER(PARTITIONBYp.name ORDERBYp.priceDESC)ASrnk FROMordersp) SELECTo.* FROMcteo WHEREo.rnk= 1; |
Result:
2- Using DISTINCT ON keyword
SELECTDISTINCTON (name) id,name,itemqty,price FROM orders ORDER BYname,priceDESC,id; |
Result:
3- Using row_number() in subquery
SELECTid,name,itemqty,price FROM ( SELECTid,name,itemqty,price ,row_number()OVER(PARTITIONBYnameORDERBYpriceDESC)ASrn FROM orders )tmp WHERE rn= 1; |
4- Using array_agg() with ORDER BY
SELECT (array_agg(idORDERBYpriceDESC))[1]ASid ,name ,max(price)ASprice FROM orders GROUP BYname; |
