Books on optimizing and refactoring SQL stored procedures Can you please recommend resources to write efficient store procedures, refactor and optimize them?

EDIT: - jcolebrand ♦

The intent of the answers to this post may be books or non-transient blogs. Please try not to refer to resources that have a tendency to disappear. 

This question is being allowed as being intentful for long term purposes, but is not a typical Stack Exchange network question. Please do not use this question as merit why another question should be permissible to be asked. Reference to it may be made as a request for evaluation on a case-by-case basis.
The best two books here are both from Itzik Ben Gan - Inside SQL Server T-SQL Querying and Inside SQL Server T-SQL Programming.

Read the Querying one first. Covers all the important information on how queries are processed, thinking in terms of sets, etc. Covers all aspects of querying. The second book goes into programming constructs when working with T-SQL. Amazing books.