Structured Query Language (SQL) is a standard programming language used for managing the relational database in order to perform different operations on the data stored in these databases.
The first time it was developed in the 1970s, SQL is regularly used not just by database administrators as well as developers who write scripts for data integration and data analysts seeking to create and run analytics queries.
The word SQL refers to the pronunciation as ess-kew’ellor successor.
SQL is used to describe the following reasons
- Modifying tables and indexes in databases;
- including, updating and delete rows of data and
- extracting specific information inside relational database management systems ( RDBMSys) This data can be used to aid in analysis, transaction processing as well as other applications that require communication with the database.
SQL queries as well as other operations are composed of commands that are written as statements and are then incorporated into software that allows users to modify, add or access information from databases tables.
Tables are the most fundamental element of a database. It comprises columns and rows of information. A table can hold records and each record is kept in one row in the table. Tables are by far the most popular type of database objects or structures that store or reference information in relational databases.
Other kinds of database objects comprise the following:
- Views are the logical representations of information gathered using one or more databases tables.
- Indexes are lookup tables that aid in speeding up the lookup of databases.
- Reports comprise of information taken from one or more tables, generally the data is a subset that is selected according to the criteria used to search for it.
Each column of the table is linked to a particular type of data , for instance, customer’s address or name — every row also contains an associated data value for the column that intersects it.
SQL Standard and custom extensions
The official SQL Standard was adopted by American National Standards Institute ( ANSI) in 1986, and an International Organization for Standardization ( ISO) adopting the standard in 1987.
Updates to SQL standard are released every few years. SQL standard are released every couple of years, with the most recent one was released in 2016. The most common way to refer towards an ISO regular version would be to use one of the standards bodies — ISO/IEC, and then the ISO Standard number followed by a colon, and the year of publication. The most current ISO Standard for SQL is ISO/IEC9075:2016.
Both open and proprietary RDBMSes designed around SQL are accessible for use by businesses. SQL-compliant products for database servers include the following:
- Microsoft SQL Server
- Oracle Database
- IBM Db2
- SAP HANA
- SAP Adaptive Server
- Oracle MySQL
- open source PostgreSQL
SQL commands as well as syntax
SQL is fundamentally a programming language developed for accessing, editing and removing information in relational database. As a language for programming, SQL comes with commands and the syntax used to issue the commands.
SQL commands are classified into various types, which include the following:
- Data Definition Language (DDL) commands are also referred to as Data Definition Commands because they create data tables.
- Data Manipulation Language (DML)commands are used to modify data in existing table by adding altering or eliminating data. Contrary to DDL commands, which specify how information is retained, DML commands are used to manipulate tables created by DDL commands.
- Data Query Language comprises just the SELECT command. It is that is used to extract specific data from tables. The command can be associated with DML commands.
- Data Control Language commands can be employed to grant or deprive access rights to users.
- Transaction Control Language commands can be used to alter the state of data , for example to COMMIT changes to transactions or ROLLBACK transactions that have changed.
SQL syntax, which is the set of rules that govern the way SQL declarations are presented and formatted is like the other languages of programming.
A few elements of SQL syntax are as follows:
- SQL statements begin with a SQL command and finish with the semicolon ( ;) For instance “SELECT * FROM customers”; This SQL statement is a way to extract all of the data from the customer table.
- SQL queries are not affected by case, which means it is possible to write them with uppercase, lowercase or a combination of both. It is however common to write SQL words — command or control operators in all caps and table/column names with lower case. The words in the statement may be treated as case-sensitive with quotes, and the two statements below yield the same results. Choose FROM customers; choose from CUSTOMERS. Both statements are distinct in that they Choose from customers and SELECT from “Customers”;
- SQL queries are terminated by a semicolon. This means that more complicated statements can be rendered on many lines, for example, this for SELECT name, telephone and age FROM customers. This command will select the the columns named name, telephone and age within the table customer.
- SQL statements can be incorporated into program flow control, meaning that the statement can include rows and tables -as in the preceding instance — perform operations on the data in the columns. For instance the following command chooses the name, number, birthdate and date of birth for all customers over 21: SELECT names telephone, name, age FROM customers whose age is greater than 21 years old;
SQL-on-Hadoop toolkits
SQL-on-Hadoop query engines are the latest variant of SQL that allows organizations with big data-centric architectures built on Hadoop databases to utilize SQL as an underlying query language.
It also allows database professionals to work with an easy query language, instead of using more complicated and less well-known languages particularly MapReduce, the MapReduce programming environment that is used for creating batch processing applications.
SQL security
SQL servers are susceptible to the same security vulnerabilities as other enterprise software, such as inadequate authentication, unsecure design, incorrect configuration, and other security problems. But, SQL injection was first discovered in 1998, is still the most prevalent security concerns in SQL systems.
SQL injection attacks generally exploit vulnerabilities in systems that do not have data submissions checked and cleaned to eliminate the risk of malicious code being in the data.
Skills in SQL and the related professions
SQL abilities can help many professions, not only those of database administrators data warehouse developers, database architects and other professionals whose jobs are directly dependent on SQL.
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