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I'm using InnoDB Plugin in the Barracuda file format with:
ROW_FORMAT=DYNAMIC
If I define a field as VARCHAR(255), and then insert a record that has a NULL value for that field, will that record still use 255 bytes in storage for the VARCHAR field? Or will there be no wasted storage space?
On a related note, if I define a field as INT then presumably every record will still use 32 bits for that field even if the value for it is NULL. Is that correct?
Thanks
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But if you store that NULL value in a variable-length column such as a column with VARCHAR data type, it will consume only two bytes from the column's length. Using Sparse Columns, NULL value will not consume any space regardless of using fixed-length or variable-length columns.
While a NULL itself does not require any storage space, NDB reserves 4 bytes per row if the table definition contains any columns allowing NULL , up to 32 NULL columns. (If an NDB Cluster table is defined with more than 32 NULL columns up to 64 NULL columns, then 8 bytes per row are reserved.)
Answer: No, Each null value only uses one bit on disk. In the scheme of things, having a few null columns will not have a major impact on the disk usage. If your database table has 30 such default null fields, it would still only be 30 bits per row.
Varchar(max) stores a maximum of 2,147,483,647 characters. But, varchar(50) keeps the 50 character space even if you don't store 50 characters. but varchar(max) is flexible to any size. size doesn't matter.
I think this should answer your question -
An SQL NULL value reserves one or two bytes in the record directory. Besides that, an SQL NULL value reserves zero bytes in the data part of the record if stored in a variable length column. In a fixed-length column, it reserves the fixed length of the column in the data part of the record. Reserving the fixed space for NULL values enables an update of the column from NULL to a non-NULL value to be done in place without causing fragmentation of the index page.
Please check more on data-type storage requirements and InnoDB physical row structure
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