I have doubts over null values.Therefore can you please explain me briefly what is a null value in sql and can we use null values at any place in sql tables?
SQL Null Values – Are Null Values Allowed in Any Column?
nullsql-standard
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Best Answer
Allowing Null Values
Microsoft SQL Server's definition of NULL:
SET ANSI_NULLS setting can change the behavior of NULL. In future versions this setting will be ON by default and you will not be able to turn it off. Details here: https://docs.microsoft.com/en-us/sql/t-sql/statements/set-ansi-nulls-transact-sql
This is an article which go in depth about NULL. https://www.simple-talk.com/sql/t-sql-programming/how-to-get-nulls-horribly-wrong-in-sql-server/
Few example of NULL in TSQL here.