Incorrect Datatype Selection in SQL

Incorrect datatype can cause many issues in sql. Below is the list compiled from many places, Mainly from Thomas Larock’s webcast.

Disk Storage
РLonger Maintenance (Index Rebuild, Reorganize, Unnecessary LOB data, prevents online index rebuilds up to 2008 R2 etc.)
– Longer Recovery
– Longer Backups
– Extra Physical I/O
– Hidden Cost when clustered key is long which is not needed. All non-clustered indexes include the clustering key

Memory– Extra Bytes need to read into Buffer
– Extra Logical I/O

– High chance of Implicit Conversion
– High Memory Grant needed as some other query might wait for memory grant. This can cause plan go serial
– 14 byte identifier added in case of triggers

What’s Remedy

– Compression ( Only in Enterprise Edition)
– Change datatype using script
– Always use backup Compression


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