Sql null not null

For this reason, any expression treating null as a value must fail. In this case, it will not match. This is also the case if you try the following:.

Specifically it is not comparing values, but rather it seeks out missing values. Finally, as regards the! It was added to make programmers from some languages feel more at home. I would like to suggest this code I made to find if there is a change in a value, i being the new value and d being the old although the order does not matter. For that matter, a change from value to null or vice versa is a change but from null to null is not of course, from value to another value is a change but from value to the same it is not.

NULL is not anything NULL does not equal anything. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Asked 10 years, 9 months ago. Active 5 months ago. Viewed k times. Could someone please explain the following behavior in SQL?

Ben Maxim Gershkovich Maxim Gershkovich Add a comment. Active Oldest Votes. Uddhav P. Gautam 6, 3 3 gold badges 42 42 silver badges 58 58 bronze badges.

Thomas: Oracle didn't support! My belief is MySQL is similar, starting support in 4. That would seem to suggest that! Here is a quick and dirty version that works on Oracle : select sum case a when null then 1 else 0 "Null values", sum case a when null then 0 else 1 "Non-null values" from us.

Similar syntax would work in SQL Server as well. Irrelevant for small tables, very important for huge ones. Single quotes, not doubles. SQLServer uses an index scan for this query vs two index seeks using a union. On a table with This did not work for me in Oracle 11g. The version user posted with "case when a is null then 1 else 0 end" was the syntax that worked. Show 3 more comments. EvilTeach EvilTeach Good gravy, man, look at the execution plans for these queries.

I don't have a database handy to look, but either the column is indexed or not. If it is, it happens via a range scan, otherwise, you are pretty much left with a full table scan. Your milage may very. After that, full scans are initiated. In this case, you'll get the scan at least once, if not twice. MichaelChirico Ariful Haque Ariful Haque 9 9 silver badges 10 10 bronze badges. Yada Abe Voelker Abe Voelker 27k 14 14 gold badges 78 78 silver badges 97 97 bronze badges. Starnuto di topo Starnuto di topo 2, 3 3 gold badges 27 27 silver badges 51 51 bronze badges.

Sven Rojek 4, 2 2 gold badges 33 33 silver badges 55 55 bronze badges. Amal Hari Amal Hari 31 2 2 bronze badges. Rodrigo Prazim Rodrigo Prazim 7 7 silver badges 14 14 bronze badges. Try this.. Amit Phaltankar 2, 2 2 gold badges 18 18 silver badges 33 33 bronze badges.

Find centralized, trusted content and collaborate around the technologies you use most. Connect and share knowledge within a single location that is structured and easy to search. What are the advantages of using one instead of the other?

If you need to represent unknown data in a column, you make it nullable. If you will always have data in the column, it's better to make it not nullable, as. Which means you have to specify a value for that field when inserting a record.

NULLs are not the same as empty strings. Here are a couple of advantages of not using NULLs. You save the space for the bit used to differentiate the NULL value. Sometimes, NULLs are needed, particularly when you are inserting incomplete records. This is good practice when applied correctly because you have to be careful with null values in tables when doing operations like joins because no null is equal to any other null.

Stack Overflow for Teams — Collaborate and share knowledge with a private group. This much is obvious, and row sizes will increase as a result of these changes, but those are expected changes. NULL and empty string both take up the same space zero bytes , but are they treated identically by the query optimizer? In general, yesfor The result can be hash joins and worktables with overly inflated sizes, resulting directly from unusually large estimated row sizes when a NOT NULL empty string column is used vs.

A great deal can be said about what seems like such a simple topic. NULL is special in the world of database design, and understanding how it works and is used in the context of your data will go a long way towards ensuring that you make the best decisions possible.

Those smart decisions early on will prove valuable years later when all of the TSQL that has been written based on them is intuitive, scalable, and easy to update. Log in or register to rate. Join the discussion and add your comment. The key to working with null values properly is to accommodate them consistently. Learn a few tricks that will help you do just that. Missing data is a difficult and common problem to solve. In this article, Joe Celko explains several approaches to deleting or replacing missing data.

Introduction When designing a new database, one of the first decisions we make it to define our columns. Will be a blank image by default. For scenarios like this, there must be a way to indicate that the ID is inapplicable, either with NULL or some alternative flag or ID that provides meaning to the given situation. End dates for ongoing tasks.

Text fields that are displayed directly in the application.