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The Art of PostgreSQL

Solution Review: Understanding Nulls

Explore how to identify and manage null values in SQL queries within PostgreSQL. Learn to use the IS NULL operator to test for nulls and apply aggregation functions to count non-null records accurately. This lesson helps you gain practical skills for handling null data effectively in database applications.

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Task 1

You were asked to write a query to list the output using the SQL operator is null for the values true, false, and null.

Solution

The solution for the challenge is given below. Click the “Run” button in the following widget to see the output of the code.

PostgreSQL
/***************************************************/
/*****     Write a query to list the output    *****/
/*****   using the SQL operator "is null" for  *****/
/*****       values true, false, and null.     *****/
/***************************************************/
select a::text as val_a,
       (a is null)::text as "is null"
  from (values(true),(false),(null)) t1(a);
/***************************************************/

Explanation

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