SQL: Difference between revisions
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This article documents standard SQL. For database-specific extensions, we'll link to the databases-specific DML operations page. | This article documents standard SQL. For database-specific extensions, we'll link to the databases-specific DML operations page. | ||
SQL is a non-procedural language | SQL is a standard non-procedural language designed to work with relational databases, allowing the users to interact with the database instance by issuing [[#SQL_Schema_Statements_(DDL)|schema statements]], [[#SQL_Data_Statements_(DML)|data statements]] and [[#SQL_Transaction_Statements|transaction statements]]. | ||
SQL statements define the necessary inputs and outputs for the database interaction, but it does not define how the statements should be executed. The details of the execution are left to the database engine component known as the optimizer. The optimizer parses the SQL statements and depending on how the tables are configured and what [[SQL_Indexes#Overview|indexes]] exist, it decides the most efficient execution path. Most database engines will allow you to influence the optimizer's decisions by accepting optimizer hints. | |||
The first standard for the SQL language was published by the American National Standards Institute (ANSI) in 1986. Subsequent refinements led to new releases of the SQL standard in 1989, 1992, 1999, 2003, 2006, 2008, 2011, and 2016. | |||
==Entity | =<span id='Table'></span>Relational Database Terminology= | ||
In a relational model, data is stored in a set of [[Relational_Databases#Table_(Relation)|tables]], also known as [[Relational_Databases#Table_(Relation)|relations]]. Within a relation, data is organized in [[Relational_Databases#Row|rows]] ([[Relational_Databases#Record_(Row)|records]]) and [[Relational_Databases#Column|columns]]. Each row describes an [[Relational_Databases#Entity|entity]]. Each is uniquely identified by a [[Relational_Databases#Primary_Key|primary key]]. The rows may contain columns that are copies of other tables' primary keys. These are knowns as [[Relational_Databases#Foreign_Key|foreign keys]] and are used in [[SQL_Querying_Multiple_Tables#Join|joining]] related data together. | |||
Also see: {{Internal|Relational_Databases#Table|Relational Databases}} | |||
==Result Set== | ==Result Set== | ||
The result of an [[SQL_SELECT#Overview|SQL query]], known as a '''result set''', is also a [[Relational_Databases#Table_(Relation)|table]] maintained in memory. | |||
==View== | ==View== | ||
=SQL Schema Statements (DDL)= | =SQL Schema Statements (DDL)= | ||
SQL schema statements are used to define the data structures stored in the database. This SQL subset is also known as Data Definition Language (DDL). All database elements (tables, constraints, etc.) create with the SQL schema statements are stored in a special set of table called the '''data dictionary''', or '''metadata'''. Also see: {{Internal|SQL_Database_Metadata#Overview|Database Metadata}} | |||
==<span id='CADT'></span><tt>CREATE | ALTER | DROP TABLE</tt>== | |||
{{Internal|SQL_CREATE_ALTER_DROP_TABLE#Overview|<tt>CREATE</tt> | <tt>ALTER</tt> | <tt>DROP</tt> <tt>TABLE</tt>}} | |||
</ | |||
= | =SQL Data Statements (DML)= | ||
SQL data statements are used to manipulate the data structures perviously defined using the [[#SQL_Schema_Statements_(DDL)|SQL schema statements]]. This SQL subset is also known as Data Manipulation Language (DML). | |||
==<tt>INSERT</tt>== | ==<tt>INSERT</tt>== | ||
{{Internal|SQL_INSERT#Overview|<tt>INSERT</tt>}} | |||
==<tt>UPDATE</tt>== | ==<tt>UPDATE</tt>== | ||
< | {{Internal|SQL_UPDATE#Overview|<tt>UPDATE</tt>}} | ||
==<tt>DELETE</tt>== | ==<tt>DELETE</tt>== | ||
< | {{Internal|SQL_DELETE#Overview|<tt>DELETE</tt>}} | ||
==<span id='SELECT'></span>Queries with <tt>SELECT</tt>== | ==<span id='SELECT'></span>Queries with <tt>SELECT</tt>== | ||
{{Internal|SQL_SELECT#Overview|Queries with <tt>SELECT</tt>}} | {{Internal|SQL_SELECT#Overview|Queries with <tt>SELECT</tt>}} | ||
=SQL Transaction Statements= | =SQL Transaction Statements= | ||
The SQL transaction statements are used to begin, end, and rollback transactions. | |||
{{Internal|SQL_Transaction_Statements#Overview|Transaction Statements}} | |||
=Data Types= | =Standard SQL Data Types= | ||
{{Internal|SQL_Data_Types#Overview|Standard SQL Data Types}} | |||
=SQL <tt>NULL</tt>= | =SQL <tt>NULL</tt>= | ||
| Line 63: | Line 57: | ||
</font> | </font> | ||
=Indexes= | =Indexes= | ||
{{Internal|SQL_Indexes#Overview|SQL Indexes}} | |||
=Constraints= | =Constraints= | ||
{{Internal|SQL_Constraints#Overview|SQL Constraints}} | |||
=Set Operations= | =Set Operations= | ||
=SQL Conditional Logic= | =SQL Conditional Logic= | ||
Revision as of 23:50, 22 May 2024
External
- Learning SQL, 3rd Edition by Alan Beaulieu
Internal
Overview
This article documents standard SQL. For database-specific extensions, we'll link to the databases-specific DML operations page.
SQL is a standard non-procedural language designed to work with relational databases, allowing the users to interact with the database instance by issuing schema statements, data statements and transaction statements.
SQL statements define the necessary inputs and outputs for the database interaction, but it does not define how the statements should be executed. The details of the execution are left to the database engine component known as the optimizer. The optimizer parses the SQL statements and depending on how the tables are configured and what indexes exist, it decides the most efficient execution path. Most database engines will allow you to influence the optimizer's decisions by accepting optimizer hints.
The first standard for the SQL language was published by the American National Standards Institute (ANSI) in 1986. Subsequent refinements led to new releases of the SQL standard in 1989, 1992, 1999, 2003, 2006, 2008, 2011, and 2016.
Relational Database Terminology
In a relational model, data is stored in a set of tables, also known as relations. Within a relation, data is organized in rows (records) and columns. Each row describes an entity. Each is uniquely identified by a primary key. The rows may contain columns that are copies of other tables' primary keys. These are knowns as foreign keys and are used in joining related data together.
Also see:
Result Set
The result of an SQL query, known as a result set, is also a table maintained in memory.
View
SQL Schema Statements (DDL)
SQL schema statements are used to define the data structures stored in the database. This SQL subset is also known as Data Definition Language (DDL). All database elements (tables, constraints, etc.) create with the SQL schema statements are stored in a special set of table called the data dictionary, or metadata. Also see:
CREATE | ALTER | DROP TABLE
SQL Data Statements (DML)
SQL data statements are used to manipulate the data structures perviously defined using the SQL schema statements. This SQL subset is also known as Data Manipulation Language (DML).
INSERT
UPDATE
DELETE
Queries with SELECT
SQL Transaction Statements
The SQL transaction statements are used to begin, end, and rollback transactions.
Standard SQL Data Types
SQL NULL
NULL in conditions.