How to use this textbook
If you just started studying SQL(Structured Query Language) is a database computer language designed for the retrieval and management of data in relational database management systems (RDBMS), database schema creation and modification, and database object access control management.SQL, it is advisable to begin with Part II that deals with the syntax of the SELECT statement. Each chapter here contains references to exercise numbers recommended for a better comprehending of the corresponding material. After that, go on with Part I, which will help you to get over difficulties in solving exercises and to understand some more subtle aspects of the language. Chapter 6 covers data modification statements. Currently, there are no exercises for these statements in the book (although we plan to include them eventually), because they are rather simple, and more complex constructs only can come up here as a result of using subqueries. However, there is a sufficient number of examples in the book, which, along with solving exercises on SQL-EX.RU, will allow you to fully understand the suggested material.
If you have a fairly good knowledge of SQL, start with Part I, using Part II as a reference manual on specific SELECT statement clauses and their specific implementation features (currently, MS A database management system (DBMS) by Microsoft Corporation.SQL Server 2012 is used). Whether you need to read other chapters of this book depends on your knowledge level; I honestly hope they will prove useful to you, as well.
I recommend you first read the description of the subject area modeled by the sample database and scrutinize the respective database schema. Then, look at the “erroneous” solution and try to locate the mistake and fix it yourself, executing the query after that. Finally, read the explanation in the book. You can check whether you understood it correctly using the SQL-EX.RU services.
If everything is clear to you without any explanation, you don’t really need this book. In this case, feel free to join
There is a query efficiency estimation service on the site. It will help you to solve problems not just correctly, but optimally (that is, to improve the performance of your queries to make them consume as less computing resources as possible).