Structured Query Language (SQL) is the standard language used for communicating with databases. This language allows performing the tasks of retrieving specific data from a database or updating it. The tutorial under consideration not only provides instructions for the basic SQL commands but also outlines the possible ways for their practical implementation while working with the SQL Interpreter.
The tutorial starts with exploring the structure of a relational database and the tables contained in them. A sample table is provided for demonstrating the attributes which can be included in the rows and columns. The following sections are devoted to the main statements used in SQL for retrieving and updating the data. The first of the discussed statements is the select statement used to form a query and retrieve specific data matching the defined criteria. The tutorial provides an example of a simple select statement and outlines the most effective ways of selecting the keywords which would allow retrieving the desirable data. Thus, the keyword from is used to identify the table from which the data will be retrieved, while an optional keyword where specifies the criteria which will be used for selecting the data. The sign “*” means retrieving data from all columns. The following discussed item is the create a statement which is used for creating a new object, such as a table, for example. The insert statement is used for adding new rows of data into the tables. The keyword inserted into will help specify the name of a specific table to which data should be added. The update statement is used for changing the data which matches the chosen criteria. Careful construction of the where clause in this statement is essential to specify the criteria for selecting the records which need to be changed. The delete statement allows deleting certain records or even the whole rows from the tables. The criteria for selecting the data which is to be deleted are defined in the delete from clause. It should be noted that if the where clause is left spare, all the records would be deleted. It means that careful construction of the where clause is essential to the successful performance of the delete command. The drop a table statement allows deleting an entire table. It is important to distinguish between the delete and drop a table commands. The first of them means deleting only all the records from the table but leaving the table itself and the corresponding attributes. The latter command in its turn allows removing not only all the records but also the table definition and all its rows with their constraints. It is valuable that the tutorial contains samples of various types for each of the statement and statement exercises with answers to them which would allow using the acquired materials in practice for developing the corresponding skills.
The SQL Course 2 guideline puts a special emphasis upon the advanced features of the select command which were not covered in the first part of the course. Significantly, all the discussed features and clauses are compliant with the requirements set by the American National Standards Institute for SQL. It means that knowledge of these advanced features is critical for the present-day specialists working with Oracle, MySQL, Sybase or any other databases compliant with SQL. For instance, the joins keyword which was omitted when the select statement was discussed in the first part of the tutorial, allows selecting data from more than one table at a time. The joins clause is included in the select statement in case if there is more than one table specified after the keyword from. Discussing the syntax of the select statement, the authors of the tutorial admit that the provided sample is expected to work with most database systems though certain deviations are possible. Thus, it is significant that this tutorial does not claim to be exhaustive, and providing the basic info on the main SQL statements, encourages the professionals to continue their work by consulting the specific database documentation.
The SQL tutorial under consideration will be useful for beginners who want to learn the ABC of SQL programming and the specialists who already know the basics of this language and can use this course as a refresher if it is necessary. The method of proceeding from the simple to more complex was effective for explaining rather complicated issues of SQL programming. Using accessible language and drawing the readers’ attention to the most significant points, this tutorial can be used as a step-by-step guideline for those who have to retrieve and/or update data from relational databases in their daily work.
In general, it can be concluded that the accessible language and the logical structure along with the combination of the theoretical materials with samples and practical exercises are the main advantages of the discussed online SQL training. Moreover, the second part of the tutorial focusing on the advanced features of the select statement allows the specialists who have already obtained the basic information to deepen their knowledge of the opportunities opened up by the SQL Interpreter.
Reference
Welcome to SQLCourse.com. n.d. Interactive online SQL training.