SQL stands for Structured Query Language and is a computer language that we use to interact with a relational database. SQL is a tool for organizing, managing, and retrieving archived data from a computer database. The original name was given by IBM as Structured English Query Language, abbreviated by the acronym SEQUEL. When data needs to be retrieved from a database, SQL is used to make the request. The DBMS processes the SQL query retrieves the requested data and returns it to us. Rather, SQL statements describe how a collection of data should be organized or what data should be extracted or added to the database.
In common usage, SQL encompasses DDL and DML commands for CREATE, UPDATE, modified, or other operations on database structure.
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What are the characteristics of SQL?
- SQL may be utilized by quite a number of users, which include people with very little programming experience.
- SQL is a non-procedural language.
- We can without difficulty create and replace databases in SQL. It isn’t a time-consuming process.
- SQL is primarily based totally on ANSI standards.
- SQL does now no longer have a continuation individual.
- SQL is entered into the SQL buffer on one or more lines.
- SQL makes use of a termination individual to execute instructions immediately. It makes use of features to carry out a few formatting.
- It uses functions to perform some formatting.
Uses of SQL
- Data definition: It is used to define the structure and organization of the stored data and the relationships among the stored data items.
- Data retrieval: SQL can also be used for data retrieval.
- Data manipulation: If the user wants to add new data, remove data, or modifying in existing data then SQL provides this facility also.
- Access control: SQL can be used to restrict a user’s ability to retrieve, add, and modify data, protecting stored data against unauthorized access.
- Data sharing: SQL is used to coordinate data sharing by concurrent users, ensuring that changes made by one user do not inadvertently wipe out changes made at nearly the same time by another user.
SQL also differs from other computer languages because it describes what the user wants the computer to do rather than how the computer should do it. (In more technical terms, SQL is a declarative or descriptive language rather than a procedural one.) SQL contains no IF statement for testing conditions, and no GOTO, DO, or FOR statements for program flow control. Rather, SQL statements describe how a collection of data is to be organized, or what data is to be retrieved or added to the database. The sequence of steps to do those tasks is left for the DBMS to determine.
SQL Rules
- A ‘;’ is used to end SQL statements.
- Statements may be split across lines, but keywords may not.
- Identifiers, operator names, and literals are separated by one or more spaces or other delimiters.
- A comma (,) separates parameters without a clause.
- A space separates a clause.
- Reserved words cannot be used as identifiers unless enclosed with double quotes.
- Identifiers can contain up to 30 characters.
- Identifiers must start with an alphabetic character.
- Characters and date literals must be enclosed within single quotes.
- Numeric literals can be represented by simple values.
- Comments may be enclosed between /* and */ symbols and maybe multi-line.
Why SQL?
- SQL is an interactive question language. Users type SQL instructions into an interactive SQL software to retrieve facts and show them on the screen, presenting a convenient, easy-to-use device for ad hoc database queries.
- SQL is a database programming language. Programmers embed SQL instructions into their utility packages to access the facts in a database. Both user-written packages and database software packages (consisting of document writers and facts access tools) use this approach for database access.
- SQL is a client/server language. Personal computer programs use SQL to communicate over a network with database servers that save shared facts. This client/server architecture is utilized by many famous enterprise-class applications.
- SQL is Internet facts access language. Internet net servers that interact with company facts and Internet utility servers all use SQL as a widespread language for getting access to company databases, frequently through embedding SQL databases get entry to inside famous scripting languages like PHP or Perl.
- SQL is a distributed database language. Distributed database control structures use SQL to assist distribute facts throughout many linked pc structures. The DBMS software program on every gadget makes use of SQL to speak with the opposite structures, sending requests for facts to get entry to.
- SQL is a database gateway language. In a pc community with a mixture of various DBMS products, SQL is frequently utilized in a gateway that lets one logo of DBMS speak with every other logo. SQL has for this reason emerged as a useful, effective device for linking people, pc packages, and pc structures to the facts saved in a relational database.
What are SQL commands?
Developers use structured query language (SQL) commands, which are specific keywords or SQL statements, to work with data stored in relational databases. The following are categories for SQL commands.
1. Data Definition Language
- SQL commands used to create the database structure are known as data definition language (DDL). Based on the needs of the business, database engineers create and modify database objects using DDL. The CREATE command, for instance, is used by the database engineer to create database objects like tables, views, and indexes.
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Command |
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1. CREATE Creates a new table, a view of a table, or other object in the database. |
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2. ALTER Modifies an existing database object, such as a table |
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DROP Deletes an entire table, a view of a table, or other objects in the database. |
2. Data Manipulation Language
- A relational database can be updated with new data using data manipulation language (DML) statements. The INSERT command, for instance, is used by an application to add a new record to the database.
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Command |
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1. SELECT Retrieves certain records from one or more tables. |
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2. INSERT Creates a record. |
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3. UPDATE Modifies records. |
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4. DELETE Deletes records. |
3. Data Query Language
- Data retrieval instructions are written in the data query language (DQL), which is used to access relational databases. The SELECT command is used by software programs to filter and return particular results from a SQL table.
4. Data Control language
- Data control language (DCL) is a programming language used by database administrators to control or grant other users access to databases. For instance, they can allow specific applications to manipulate one or more tables by using the GRANT command.
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Command |
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1. GRANT Gives a privilege to the user. |
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2. REVOKE Takes back privileges granted by the user. |
5. Transaction Control Language
- To automatically update databases, the relational engine uses transaction control language (TCL). For instance, the database can reverse a mistaken transaction using the ROLLBACK command.
SQL Injection
A cyberattack known as SQL injection involves tricking the database with SQL queries. To retrieve, alter, or corrupt data in a SQL database, hackers use SQL injection. To execute a SQL injection attack, for instance, they might enter a SQL query in place of a person’s name in a submission form.
What is SQL Server?
Microsoft’s relational database management system, which uses SQL to manipulate data, is formally known as SQL Server. There are various editions of the MS SQL Server, and each is tailored for particular workloads and requirements.
Finally, SQL is not a particularly structured language, especially when compared with highly structured languages such as C, Pascal, or Java. Instead, SQL statements resemble English sentences, complete with “noise words” that don’t add to the meaning of the statement but make it read more naturally. SQL has quite a few inconsistencies and also some special rules to prevent you from constructing SQL statements that look perfectly legal but that don’t make sense.
Despite the inaccuracy of its name, SQL has emerged as the standard language for using relational databases. SQL is both a powerful language and one that is relatively easy to learn. So, SQL is a database management language. The database administrator is answerable for handling a minicomputer or mainframe database and makes use of SQL to outline the database shape and manipulate get entry to the saved data.
How SQL Works?
A server machine is used in the implementation of the structured query language (SQL), processing database queries and returning results. The following are some of the software elements that the SQL process goes through.
- Parser: The parser begins by replacing some of the words in the SQL statement with unique symbols, a process known as tokenization. The statement is then examined for the following:
- Correctness: The parser checks to see if the SQL statement complies with the rules, or SQL semantics, that guarantee the query statement’s accuracy. The parser, for instance, looks to see if the SQL command ends with a semicolon. The parser returns an error if the semi-colon is absent.
- Authorization: The parser additionally confirms that the user executing the query has the required permissions to alter the relevant data.
- Relational Engine: The relational engine, also known as the query processor, develops a strategy for efficiently retrieving, writing, or updating relevant data. For instance, it looks for queries that are similar to others, uses earlier data manipulation techniques, or develops a new one. Byte code, an intermediate-level representation of the SQL statement, is used to write the plan. To efficiently perform database searches and modifications, relational databases use byte code.
- Storage Engine: The software element that interprets the byte code and executes the intended SQL statement is known as the storage engine, also known as the database engine. The data in the database files on the physical disc storage is read and stored. The storage engine delivers the outcome to the requesting application after completion.