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: