SQL

Pregunta	Respuesta
Database	a collection of items that can exist over a long period of time
records	representations of physical or conceptual objects
record’s attributes	multiple information or data, such as individual name, job title, company name and address, phone number and more
metadata	is the information that defines or describes the data’s structure within the given database (defined as a self-describing entity), stored in a region called data dictionary
database categories	personal, workgroup or departmental, and enterprise
Personal Database	conceptualized and designed by a single person on a stand-alone computer.
Workgroup/Departmental Database	designed and created by individuals of a single workgroup or department within a certain organization.
Enterprise Database	this type is conceptualized and created to handle the entire flow of information of very large organizations.
relational database	is an entity consisting of logical units known as tables, how the tables are related to each other defines their relationships.
common key	links the tables to one another in a relational database
Database Management Systems (DBMS)	important programming tool that consists of a set of programs that define, manage and process databases and all applications associated to them
types of users that work on DBMS	conventional user who retrieves or modifies data and the administrator who is responsible for maintaining the structure of the database
Schema	also called the conceptual view or the complete logical view that defines the entire database structure and provides overall table organization, considered a metadata – stored in tables and part of the database
Domain	This specifies the set of all finite data values you can store in a particular table column or attribute, for example the STATE column can only contain the values “TX”, “NY”, “CA” and “NV”
Constraint	this sets down the rules that identify what data values a specific table attribute can contain, Together with defined table characteristics, column constraints determine its domain.
Categories of SQL Command Types	Data Definition Language (DDL), Data Manipulation Language (DML), Data Query Language (DQL), Data Control Language (DCL) , Transactional Control Commands
Data Definition Language (DDL) commands	CREATE = is responsible for building the database structure, ALTER = “changing the database structure after it has been created, DROP = destroys the database structure
Data Manipulation Language (DML) commands	INSERT =used to insert new data values into a certain table, UPDATE = used to modify or alter pre-existing data values in a table, not add or remove records, DELETE = deletes certain records or even the entire table, not data values from specific columns
Data Query Language (DQL) commands	SELECT
“Data Control Language (DCL) commands	GRANT = provides you with certain privileges, like giving you the permission to access the database, REVOKE = revokes your privileges, like removing your permission to access the database
Transactional Control Commands	COMMIT = completes a transaction by making the changes you made to the database permanent, or simply saving the transactions, ROLLBACK = restore the database system to its previous state or undo all the actions that took place in the transaction log, SAVEPOINT = works with the ROLLBACK command, wherein it creates sections or points within groups of transactions in which you will be performing the ROLLBACK command.
Data types in SQL	numeric, string, date and time, boolean
numeric	INTEGER ( -2,147,483,648 to 2,147,483,647), SMALLINT (-32,768 to +32,767), BIGINT (-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807), NUMERIC (p, s) = 'p' specifies the precision while ‘s’ is for the scale. For example, NUMERIC (6, 3) means that the number’s absolute value will only be up to 999.999 (6 total significant digits with 3 digits following the decimal point), DECIMAL (p, s) = the same as NUMERIC but rounds the number, Let us say you entered the number 123.4564, this will be rounded off to 123.456. The allocated storage size for this data type is based on the given precision, REAL, DOUBLE PRECISION (p, s), FLOAT (p, s)
string	CHARACTER (n) or CHAR (n) = n equals the number of characters or the maximum allocated length for the defined field, CHARACTER VARYING (n) or VARCHAR (n) = This is used when the data entries are of different lengths, or not constant, but you don’t want SQL to fill the remaining spaces with blanks, CHARACTER LARGE OBJECT (CLOB) = used to contain unicode character-based information that is too big to be stored as a CHARACTER type, such as large documents
date and time	DATE, TIME, DATETIME, TIMESTAMP = the same as DATETIME but the range of values is from “1970-01-01 00:00:01” UTC to “2038-01-19 03:14:07” UTC.
Boolean	This data type consists of values that are used for data comparison: TRUE, FALSE, or NULL

Siguiente

Descripción

Resumen del Recurso

Similar

	Creado por Ivan Espinosa hace más de 7 años