WGU D427 Data Management - Applications

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160 terms MoDhochesPreview WGU C 73 terms j8ni database modelA database model is a conceptual framework for database systems, with three

parts:

• Data structures that prescribe how data is organized.
• Operations that manipulate data structures.
• Rules that govern valid data.

relational modelThe relational model is a database model based on a tabular data structure. The model was published in 1970 by E. F. Codd of IBM and released in commercial products around 1980. The data structure, operations, and rules are standardized in SQL, the universal query language of relational databases.big dataThe rise of the internet in the 1990s generated big data, characterized by unprecedented data volumes and rapidly changing data structures.setA set is an unordered collection of elements enclosed in braces.tupleA tuple is an ordered collection of elements enclosed in parentheses.tableA table has a name, a fixed tuple of columns, and a varying set of rows.columnA column has a name and a data type.rowA row is an unnamed tuple of values. Each value corresponds to a column and belongs to the column's data type.data typeA data type is a named set of values, from which column values are drawn.

relational algebraThese operations are collectively called relational algebra and are the theoretical foundation of the SQL language.Relational rulesRelational rules are part of the relational model and govern data in every relational database.Business rulesBusiness rules are based on business policy and specific to a particular database.constraintsRelational rules are implemented as SQL constraints and enforced by the database system.Structured Query Language / SQLStructured Query Language (SQL) is a high-level computer language for storing, manipulating, and retrieving data.statementAn SQL statement is a complete command composed of one or more clauses.clauseA clause groups SQL keywords like SELECT, FROM, and WHERE with table names like City, column names like Name, and conditions like Population > 100000.Data Definition LanguageData Definition Language (DDL) defines the structure of the database.Data Query LanguageData Query Language (DQL) retrieves data from the database.Data Manipulation LanguageData Manipulation Language (DML) manipulates data stored in a database.Data Control LanguageData Control Language (DCL) controls database user access.Data Transaction LanguageData Transaction Language (DTL) manages database transactions.database system instanceA database system instance is a single executing copy of a database system.Personal computers usually run just one instance of a database system. Shared computers, such as computers used for cloud services, usually run multiple instances of a database system.CREATE DATABASE DatabaseNameCREATE DATABASE DatabaseName creates a new database.DROP DATABASE DatabaseNameDROP DATABASE DatabaseName deletes a database, including all tables in the database.USE DatabaseNameUSE DatabaseName selects a default database for use in subsequent SQL statements.SHOW DATABASESSHOW DATABASES lists all databases in the database system instance.SHOW TABLESSHOW TABLES lists all tables in the default database.SHOW COLUMNS FROM TableNameSHOW COLUMNS FROM TableName lists all columns in the TableName table of the default database.

SHOW CREATE TABLE TableNameSHOW CREATE TABLE TableName shows the CREATE TABLE statement for the TableName table of the default database.tableA table has a name, a fixed sequence of columns, and a varying set of rows.columnA column has a name and a data type.rowA row is an unnamed sequence of values. Each value corresponds to a column and belongs to the column's data type.cellA cell is a single column of a single row.empty tableA table without rows is called an empty table.data independenceRule 4 is called data independence.CREATE TABLEThe CREATE TABLE statement creates a new table by specifying the table name, column names, and column data types.DROP TABLEThe DROP TABLE statement deletes a table, along with all the table's rows, from a database.ALTER TABLEThe ALTER TABLE statement adds, deletes, or modifies columns on an existing table.data typeA data type is a named set of values from which column values are drawn.IntegerInteger data types represent positive and negative integers.DecimalDecimal data types represent numbers with fractional values.CharacterCharacter data types represent textual characters.Date and timeDate and time data types represent date, time, or both. Some date and time data types include a time zone or specify a time interval.BinaryBinary data types store data exactly as the data appears in memory or computer files, bit for bit.SpatialSpatial data types store geometric information, such as lines, polygons, and map coordinates.DocumentDocument data types contain textual data in a structured format such as XML or JSON.signedA signed number may be negative.unsignedAn unsigned number cannot be negative.

operator / operandsAn operator is a symbol that computes a value from one or more other values,

called operands:

• Arithmetic operators compute numeric values from numeric operands.
• Comparison operators compute logical values TRUE or FALSE.
• Operands may be numeric, character, and other data types.
• Logical operators compute logical values from logical operands.

unaryA unary operator has one operand.binaryA binary operator has two operands.expressionAn expression is a string of operators, operands, and parentheses that evaluates to a single value. Operands may be column names or fixed values. The value of an expression may be any data type.operator precedenceOperators in an expression are evaluated in the order of operator precedence, shown in the table below. Operators of the same precedence are evaluated from left to right. Regardless of operator precedence, expressions enclosed in parentheses are evaluated before any operators outside the parentheses are applied.SELECT / FROMThe SELECT statement selects rows from a table. The statement has a SELECT clause and a FROM clause. The FROM clause specifies the table from which rows are selected. The SELECT clause specifies one or more expressions, separated by commas, that determine what values are returned for each row.result tableThe SELECT statement returns a set of rows, called the result table.LIMITMySQL has a LIMIT clause that limits the number of rows returned by a SELECT statement.conditionA condition is an expression that evaluates to a logical value.WHEREA SELECT statement has an optional WHERE clause that specifies a condition for selecting rows. A row is selected when the condition is TRUE for the row values. A row is omitted when the condition is either FALSE or NULL.NULLNULL is a special value that represents either unknown or inapplicable data.NOT NULLThe NOT NULL constraint prevents a column from having a NULL value.Statements that insert NULL, or update a value to NULL, are automatically rejected. NOT NULL follows the column name and data type in a CREATE TABLE statement.IS NULL / IS NOT NULLInstead, the IS NULL and IS NOT NULL operators must be used to select NULL values. Value IS NULL returns TRUE when the value is NULL. Value IS NOT NULL returns TRUE when the value is not NULL.truth tablesThe value of logical expressions containing NULL operands is defined in truth tables.