1) FTS (Full Table Scans) are always bad and Index usage is always good.
2) Usage of dynamic SQL within the stored procedure code is always bad even for search procedures.
3) Empty Space in an index that gets created due to the DML operations do not get used.
4) Indexes should be rebuilt at regular intervals.
5) Indexes and statistics are the same thing. Also, histograms are needed only on indexed columns.
6) Usage of cursors is always bad so avoid them like the plague.
7) Truncate command cannot be rolled back because it is a non-logged operation.
8 ) Table variables in SQL Server are always only memory resident.
9) Column order in a covered index does not matter.
10) In the case of SQL Server, one can separate the clustered index from the table.
11) Only committed data gets written to the disk.
12) Logical I/Os (LIO) are not a cause of concern, only Physical IO (PIO) are.
13) Count(1) is better performing than count(*).
14) Issue frequent commits in the application to make the transaction faster and also improve concurrency.
15) Views are evil evil DB Objects that always slow down performance.