Is there any difference between IS NULL and =NULL

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I am surprised to see that IS NULL and =NULL are yielding different results in a select query. What is difference between them? When to use what. I would be glad if you can explain me in detail.

= NULL is always unknown (this is piece of 3 state logic), but WHERE clause treats it as false and drops from the result set. So for NULL you should use IS NULL

Reasons are described here: Why does NULL = NULL evaluate to false in SQL server

Understanding the difference between IS NULL and = NULL , = NULL is always unknown (this is piece of 3 state logic), but WHERE clause treats it as false and drops from the result set. So for NULL you  Extract of a relevant paragraph : Challenges. Null has been the focus of controversy and a source of debate because of its associated three-valued logic (3VL), special requirements for its use in SQL joins, and the special handling required by aggregate functions and SQL grouping operators.

To add to existing answers, it depends whether you have ANSI_NULLS on or not, when using "= NULL".

-- This will print TRUE
SET ANSI_NULLS OFF;
IF NULL = NULL
    PRINT 'TRUE'
ELSE
    PRINT 'FALSE'

-- This will print FALSE
SET ANSI_NULLS ON;
IF NULL = NULL
    PRINT 'TRUE'
ELSE
    PRINT 'FALSE'

Is there any difference between IS NULL and =NULL, Is Null and IsNull() both find null values, but you won't use them in the same way. You would use Is Null and Is Not Null in query expressions and  Null has been the focus of controversy and a source of debate because of its associated three-valued logic (3VL), special requirements for its use in SQL joins, and the special handling required by aggregate functions and SQL grouping operators.

There is a difference between IS NULL and = NULL and this is because of the three-valued-logic of SQL:

https://en.wikipedia.org/wiki/Null_%28SQL%29#Three-valued_logic_.283VL.29

Extract of a relevant paragraph:

Challenges

Null has been the focus of controversy and a source of debate because of its associated three-valued logic (3VL), special requirements for its use in SQL joins, and the special handling required by aggregate functions and SQL grouping operators. Computer science professor Ron van der Meyden summarized the various issues as: "The inconsistencies in the SQL standard mean that it is not possible to ascribe any intuitive logical semantics to the treatment of nulls in SQL." Although various proposals have been made for resolving these issues, the complexity of the alternatives has prevented their widespread adoption.

Learn the differences between Is Null and IsNull() in Access , isnull function lets you return an alternative value when an expression is null is null operator list all records that have no values. It just makes more sense to use x != null because that is more like how we would say this. You could ask me "Is x not null?" That seems more natural than "Is null not x?" It makes more sense to us.

What is the difference between IS NULL operator and ISNULL , Disclaimer: Because the syntax for filtering in QGIS works with SQL, I'm assuming here that SQL rules apply. I'm not completely sure if that's  Both are different.Null is value which is unknown. If you want to extract the null values use is null. If you want to extract blank values use = ' '

What is the difference between != NULL and IS NOT NULL in QGIS , The result of the expression in the when clause is true if both arguments are equal or both are null . If only one argument is null the result is unknown, not false. Null is a term in mathematics implying the empty / void value or quantity. It is synonymous with zero, but it may differ based on the context. Null vector is a vector with all the elements as zero, and null is also applied in the same sense to the matrices with all zero elements.

NULL -Aware Comparison: is [not] distinct from, The ISNULL and Coalesce functions are both used to replace null values with a user-defined value. So let's take a look at a practical example  Difference between Null and empty string in Python Python doesn’t have a Null string at all. Python does have a None value but it isn’t a string it is A None that can be applied to all variables – not just those which are originally defined as a string.

Comments
  • Check out the wikipedia article for additional information.
  • This is a dup of a number of questions: stackoverflow.com/questions/1843451/…
  • It is not false. It is unknown. If it was false then NOT(X = NULL) would be true. This is not the case. SQL uses 3 valued logic.
  • @Martin Smith i know about 3 state logic. but WHERE clause treats unknown as false and drop off from result set.
  • Please do not post link-only answers. Include the relevant information from the link here, so that if the target site disappears, your answer will still be useful. (This is better as a comment.)