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Why are NULLs bad in SQL?
Null values make development more difficult and bug prone. Null values make queries, stored procedures, and views more complex and bug prone. Null values take up space (? bytes based on fixed column length or 2 bytes for variable column length).
Should a database have NULL values?
NULL values are used to indicate that you could have a value, but you don’t know what that value should be yet. You can use NULL values for any data type including integers, decimals, strings, or blobs. Even though many database administrators use NULL, they usually demand that NULLs are not used for numeric values.
What is the risk of having NULL values in a numeric column?
So, allowing NULL values makes you work extra hard to get the kind of data you are looking for. From a related angle, allowing NULL values reduces your convictions about the data in your database. You can never quite be sure if a value exists or not.
Do null values take up space?
If the field is variable width the NULL value takes up no space. In addition to the space required to store a null value there is also an overhead for having a nullable column. For each row one bit is used per nullable column to mark whether the value for that column is null or not.
What happens when there are too many columns in a table?
Having too many columns results in a lot nulls (evil) and an unwieldy object the table is mapped to. This hurts readability in the IDE and hinders maintenance (increasing development costs). If you need fast reads in some cases use denormalized tables e.g. used solely for reporting or queries (search for the “CQRS” pattern).
Is there an advantage to having many columns in a database?
When it comes to really LARGE scale databases, is there actually an advantage to having a large amount of columns, despite the fact that this usually leads to many NULL values? Which is more of a performance hit: lots of columns with lots of NULLs, or fewer columns with lots of JOINs? The design of the table depends on the entity it needs to store.
Which is correct 50 columns or 100 columns?
The design of the table depends on the entity it needs to store. If all the data belongs together, then 50 columns (or even 100) might be the correct thing to do. So long as the table is normalized, there is no rule of thumb regarding size, apart from database capabilities and the need to optimize. I agree with Oded.
Is it good to have many columns in Cassandra?
In the NO-SQL world (cassandra/hbase for example) there are no constraints on the number of columns and it’s actually considered a good practice to have many columns. This also comes from the way it is stored (no gaps). Worth while investigating.