SQL is a short form of Structured Query Language. It is a domain-specific language used to design, and program the data held in RDBMS (Relational database management system). Specifically, SQL is used in data incorporating relations among entities and variables.
It is important to note that SQL is not an imperative programming language like BASIC or C. Rather, it is a set-based declarative programming language. Further, procedural programming language functionality can be added to this language by extensions to standard SQL.
In the simplest words, SQL is the language of databases. Using SQL, we can insert, update, fetch, and delete the data present in the databases.
Originally, SQL was developed at IBM by Raymond F. Buyers and D.Chamberlain. The initial version was developed in the 1970s and was earlier named SEQUEL which expanded as a structured English query language. Primarily, it was designed to modify and retrieve data stored in IBM’s original database management system.
The developers resumed working on this language in 1973 after moving to Saint Joes’ research laboratory. It was at this time that SEQUEL was changed to SQL due to some trademark issues and underwent testing at customer sites.
The first practical implementation of SQL which was commercially available, came out in 1979. Going further in the milestones, SQL was adopted by ANSI and ISO in 1989 and since then the database language has always continued evolving in the form of its new versions being published at frequent intervals, the most recent being in 2016.
Syntax and language elements
Numerous language elements combine to compose a single statement in SQL. This subdivision of several language elements in SQL includes:
- Clauses: The constituent components of queries and statements are called clauses. However, they may be optional in some cases.
- Expressions: The tables that contain any sort of data in the form of columns or rows are produced by expressions. In another way, expressions can also produce scalar values.
- Predicates: Predicates particularly specify the conditions which can be evaluated to SQL 3VL (3 valued logic), which includes three options, namely true/false/unknown. Predicates can also be present in the form of Boolean truth values that limit the effects of statements and queries. They are also used to change the program flow.
- Queries: Queries are one of the most important elements of SQL which are used in the retrieval of data based on particular criteria.
- Statements: This element of SQL has a continuous effect on data. Statements are also responsible for controlling transactions, program flow, sessions, and connections. These statements include a semicolon (;) known as a statement terminator. This semicolon is usually considered to be a standard part of SQL grammar.
- Whitespace: White spaces are considered completely insignificant in SQL so as to make the formatting of SQL code easier as well as for readability.
SQL Data types
Three types of data types are defined by SQL standard, viz-a-viz Constructed types, user-defined types, and predefined data types. Predefined data types include character types, national character types, binary types, and numeric types. These also include DateTime types, boolean types, XML, JSON, and more.
Constructor types are either ARRAY, MULTISET, ROW, or REF. The third type, user-defined types are compared to the classes in object-oriented language with their own methods, contractors, observers, overloading, overwriting, and more.
Usage and suitability
Since ANSI has regarded SQL as a standard language for relational database management systems, SQL is used by various database management systems such as Oracle, Microsoft SQL Server, Access, Ingres, Sybase, and more. In order to retrieve specific information from databases, there are some standard SQL commands that make the information retrieval work simpler.
These basic commands include select, insert, update, delete, drop, and create. Besides retrieving information from databases, SQL is also suitable for updating data on a database, creating a new database, inserting new data in the database, modifying the previous data, deleting the data from a database, creating tables in databases, or even dropping the tables.
Certain incompatibility issues result in difficulty in porting SQL code between database systems without alterations. Also, the most common implementations of SQL usually do not support basic features of standard SQL such as date or time data types.
Implementations of this language are incompatible between Wenders and they do not always follow the standards to a complete extent. The reasons for this incompatibility are many including the Complexity of the SQL standard and its use size. Secondly, the standard does not particularly mention database behavior in important areas.
Also, many database vendors already have large amounts of existing customer bases, due to which the newer versions of SQL standards find it difficult to be compatible with the prior behavior of the vendor’s database.
Criticisms and alternatives
Just like every other language, SQL also has its share of criticism in terms of its design. Critics are of the opinion that SQL diverts from its theoretical foundation in various ways. The presentation of data also differs from its relational model.
In SQL, Query results are shown in the form of a list of rows while in the relational model, the table is a set of tuples. Critics also state that due to these differences, SQL should be substituted with such a language that strictly adheres to its original foundation. The concept of Null used in SQL is also subject to criticism.
The Null is basically an indication of the absence of a value that is different from a value of zero or an empty string in a text column. The duplication of rows is also subject to popular criticism in the case of SQL. The duplication of rows also creates further problems such as difficulty in integration with other languages such as Python.
Kuldeep is the founder and lead author of ArtOfTesting. He is skilled in test automation, performance testing, big data, and CI-CD. He brings his decade of experience to his current role where he is dedicated to educating the QA professionals. You can connect with him on LinkedIn.