SQL Select Unique - sql - sql tutorial - learn sql




  • SELECT UNIQUE is an old syntax which was used in oracle description but later ANSI standard defines DISTINCT as the official keyword.
  • After that oracle also added DISTINCT but did not withdraw the service of UNIQUE keyword for the sake of backward compatibility.
  • In simple words, we can say that SELECT UNIQUE statement is used to retrieve a unique or distinct element from the table.
  • The SELECT UNIQUE construct is an Oracle-only SQL statement. It is equivalent to SELECT DISTINCT.
  • The SELECT DISTINCT statement is used to return only distinct (different) values.
  • Inside a table, a column often contains many duplicate values; and sometimes you only want to list the different (distinct) values.
  • The SELECT DISTINCT statement is used to return only distinct (different) values.
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Syntax

  • The syntax for SELECT UNIQUE is as follows:
SELECT UNIQUE "column_name"
FROM "table_name";
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Example

  • We use the following table for our example.

Table product _Information

Store_Name Sales Txn_Date
Los Angeles 1500 Jan-05-1999
San Diego 250 Jan-07-1999
Los Angeles 300 Jan-08-1999
Boston 700 Jan-08-1999
  • To select all distinct stores in Table product_Information in Oracle, we key in,
SELECT UNIQUE Sales FROM product_Information;

Result:

Sales
1500
250
300
700
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Exercises

  • For these exercises, assume we have a table called province _Sales with the following data:

Table province _Sales

province Year Orders Total_Sales
West 2013 1560 325000
West 2014 1820 380000
North 2013 790 148000
North 2014 995 185000
East 2013 1760 375000
East 2014 2220 450000
South 2013 1790 388000
South 2014 1695 360000
  • (True or False) The following two statements are equivalent in MySQL:
SELECT UNIQUE province FROM province _Sales; 
SELECT DISTINCT province FROM province _Sales;
  • Answer: False.
  • Which of the following statements are valid in Oracle?
SELECT DISTINCT Year FROM Region_Sales; 
SELECT UNIQUE * FROM Region_Sales; 
SELECT * FROM Region_Sales; 
SELECT UNIQUE Year FROM Region_Sales;
  • Answers : a), c), d).
  • What is the output for the following statement?
SELECT UNIQUE Region FROM Region_Sales WHERE Orders < 1000;
  • Answers : The result is,
REGION
North

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