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Category: Data Types

Data Types

Grant Fritchey implores you to use the correct data type:

Far too often then, the easy answer, just change the column to varchar. You can trim the time and output in exactly the format needed by the business. Problem solved and it was easy…

Well, until someone inputs “Janry 20, 2009” slightly mangling the spelling and suddenly your report looks all messed up. Or, they ask you to start filtering just the last two weeks, regardless of when the report was run and you now can’t easily dodate math on the column. Even after you get over that problem with a little formatting using CAST (along with ISDATE to try to catch all those other typos that are in the system now)  you notice that the performance is really slow so you go to put an index on the column and now you have an index key that is 50 bytes wide instead of the 3 bytes that the DATE data type would have been, making the index less efficient (not to mention, sorting the data is going to put February ahead of January, more formatting).

Read the whole thing.

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Kenneth Fisher warns against low VARCHAR sizes:

The first thing you’ll notice is that a single space is stored the same way in both columns. With an empty string, on the other hand, we see a difference. Char columns are fixed length. So even though we inserted an empty string into it we get back a single space.

The next major difference is that varchar columns require an extra two bytes of storage. So a varchar(1) column actually uses three bytes not just the one byte that char(1) does.

This is exactly the type of scenario row-level compression improves.

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