Eric Ligman has posted a nice collection of ebooks available in pdf, epub and mobi formats. The books cover Office, Office 365, SharePoint, SQL Server, System Center, Visual Studio, Web Development, Windows, Windows Azure, and Windows Server

Here is what is available for SQL Server

5 Tips for a Smooth SSIS Upgrade to SQL Server 2012
A Hitchiker’s Guide to Microsoft StreamInsight Queries
Data Mining Extensions (DMX) Reference
Data Quality Services
High Availability Solutions
Master Data Services
Monitor and Tune for Performance
Multidimensional Expressions (MDX) Reference
SQL Server Distributed Replay
Transact-SQL Data Definition Language (DDL) Reference
XQuery Language Reference
Extracting and Loading SharePoint Data in SQL Server Integration Services
Integration Services: Extending Packages with Scripting
Multidimensional Model Programming
Optimized Bulk Loading of Data into Oracle
Planning Disaster Recovery for Microsoft SQL Server Reporting Services in SharePoint Integrated Mode
SQL Server 2012 Tutorials: Reporting Services
SQL Server 2012 Tutorials: Writing Transact-SQL Statements
SQL Server Community FAQs Manual

You can get all the links from here: http://blogs.msdn.com/b/mssmallbiz/archive/2013/06/18/huge-collection-of-free-microsoft-ebooks-for-you-including-office-office-365-sharepoint-sql-server-system-center-visual-studio-web-development-windows-windows-azure-and-windows-server.aspx?Redirected=true