SQL

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Conceptos básicos de SQL
Ivan Espinosa
Flashcards by Ivan Espinosa, updated more than 1 year ago
Ivan Espinosa
Created by Ivan Espinosa over 5 years ago
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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
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