PostgreSQL: Sort result by DateTime, but the null value should be first or last

I want to sort my result by date time column in ascending order but null values should come first or vice versa. Suppose I have a table employee and it has the column appraisal_date if I sorted the result set by appraisal_date in ASC/DESC order it should be the null value come FIRST/LAST.

PostgreSQL provides keywords such as "NULLS FIRST | LAST" that help find accurate results with "ORDER BY CLAUSE."

Illustration to get the accurate result-set sort by DateTime in ascending (ASC) order but null first

First I will create an employee table

CREATETABLEemployee

(

emp_idintgeneratedalwaysasidentity,

nametext,

appraisal_datedate

);

-- Here I will insert some records

INSERTINTOemployee(name,appraisal_date)

VALUES

('Dilip','27/04/2020'),

('Mamta','28/04/2020'),

('Ashish',null),

('Naina','30/04/2020'),

('Aradhya','21/04/2020'),

('Mukesh',null);

Sort Result null first

SELECT*FROMemployeeORDERBYappraisal_dateASCNULLSFIRST;

Expected result

Illustration to get the accurate result-set sort by DateTime in descending (ASC) order but null first

SELECT*FROMemployeeORDERBYappraisal_dateDESCNULLSFIRST;

Expected Result

Illustration to get the accurate result-set sort by DateTime in descending (ASC) order but null first

SELECT*FROMemployeeORDERBYappraisal_dateASCNULLSLAST;

Expected Result

Illustration to get the accurate result-set sort by DateTime in descending (ASC) order but null first

SELECT*FROMemployeeORDERBYappraisal_dateDESCNULLSLAST;

Expected Result

To support the query with an index, make it match:

CREATEINDEXappraisal_date_indexONemployee(appraisal_dateASCNULLSFIRST);

CREATEINDEXappraisal_date_indexONemployee(appraisal_dateDESCNULLSLAST);