SQL development company in Delhi | SQL – Structured Query Language


SQL – Structured Query Language is used to interact with Relational Database Management Systems or RDBMS for short. SQL is a very old language but is still very popular for accessing and manipulating data inside a database. Every vendor has made his version of SQL. SQL used for accessing MySQL is slightly different than that used for accessing MS-SQL database. SQL is a case insensitive language but by convention the keywords of the SQL language are written in upper case letters like INSERT, SELECT, DELETE, JOIN etc. SQL based databases are fairly popular but nowadays NoSql databases like mongodb have started to gain popularity. These NoSql databases are used where billions of rows of data is involved.

SQL stand for structured query language. It a special programming language designed for managing data in relational database management system. SQL was initially developed by IBM. SQL consists of data definition language, data manipulation language and data control language. Scope of SQL are data insertion, data deletion, data manipulation and query. The first version of SQL was called SEQUEL which stands for Structured English QUERY Language. It was designed to manipulate and retrieve data stored in IBM’s original quasi-relational database management system.

Relational database management system is the way of storing information in new databases for financial record or any personal data. Databases are very important for storing information or data for future use. Databases are the backbone record in any organization. These are the storage house of user data and information of billions of websites across the world. The websites today cannot be imagined without its databases for user information. The relational database management system is managing all these user data. It is playing the biggest role in modern web technology. The social networking sites, apps and online shopping sites cannot be imagined without the databases. A simple website with signup facility also needs the database to store the information of user.

SQL is such a language which plays the game of user interaction with the site.it is so crucial that without this language the user interactive sites are meaningless. It can be said that without this language the web technology might have been locked at a state. The query language is the building block of large web sites. SQL contains several elements:

  • 1. Clauses: clauses are components of statement and queries.
  • 2. Expression: expressions produce the tables with rows and columns.
  • 3. Predicates: predicates specify the conditions that can be evaluated to SQL three value logic.
  • 4. Queries: queries retrieve the data depending upon the availability and types.
  • 5. Statements: statements gives effect on data.

The SQL queries are the basic players of data manipulation. Queries are used to store data, delete data, update data and many more purposes. These queries send the user information to the database and retrieve the same data for display. The queries are the main components of playing with data. Without these queries the interaction with user is impossible. Billions of user information are stored on databases using these queries. Insertion to deletion, retrieval to update everything is performed by the SQL queries. Queries are the running force for data. A query includes a list of columns to include the final result following the select keyword. Select is the most complex statement in SQL. Some other clauses do optional works with data.

  • 1. The FROM clause indicates the table from where data to be retrieved.
  • 2. The WHERE clause indicates the place from where data to be retrieved. It is a comparison predicate.
  • 3. The GROUP BY clause is used to project rows having common values into a smaller set of rows.
  • 4. The ORDER BY clause identifies which columns to use to sort the resulting data.
  • 5. The HAVING clause includes a predicate used to filter ROWS resulting from GROUP BY clause.

Data manipulation:

Data manipulation is the subset of INSERTING, UPDATING and DELETING of data. The INSERT query adds rows to an existing table. The DELETE query removes existing rows from the table and UPDATE query the rows in existing table. MERGE query is used to combine data of multiple tables.

Data definition:

Data definition manages the table and index structure. Basic works of definition is to CREATE, ALTER, RENAME, DROP and TRUNCATE. CREATE instruction creates an object in the database. The ALTER instruction modifies the structure of an existing object. The TRUNCATE instruction deletes all the data from a table in very fast way. The DROP instruction deletes an object in database which cannot be retrieved.

Data types in SQL:

Character Strings: CHARACTER (n): fixed with n character string. CHARACTER VARYING (n): variable width string with a maximum size of n character. Number: INTEGER, SMALL INT AND BIG INT, FLOAT, REAL and DOUBLE PRECISON. Bit strings: BIT (n): an array of n bits. BIT VARYING (n) an array of up to n bits. Date and Time: Date: Date is used for date value. Time: Time is used for time value.