WGU D426 Study Guide: Key SQL Commands and
Database Concepts Explained 100% Correct | Graded A+ |
New 2025-2026 Update
A database application is software that helps business users interact with database systems.
Database roles
People interact with databases in a variety of roles:
● A database administrator is responsible for securing the database system against unauthorized
users. A database administrator enforces procedures for user access and database system
availability.
● Authorization. Many database users should have limited access to specific tables, columns, or
rows of a database. Database systems authorize individual users to access specific data.
● Rules. Database systems ensure data is consistent with structural and business rules. Ex: When
multiple copies of data are stored in different locations, copies must be synchronized as data is
updated. Ex: When a course number appears in a student registration record, the course must
exist in the course catalog.
● The query processor interprets queries, creates a plan to modify the database or retrieve data,
and returns query results to the application. The query processor performs query optimization
to ensure the most efficient instructions are executed on the data.
● The storage manager translates the query processor instructions into low-level file-system
commands that modify or retrieve data. Database sizes range from megabytes to many
terabytes, so the storage manager uses indexes to quickly locate data.
● The transaction manager ensures transactions are properly executed. The transaction manager
prevents conflicts between concurrent transactions. The transaction manager also restores the
database to a consistent state in the event of a transaction or system failure.
MongoDB MongoDB NoSQL Open source 5
● INSERT inserts rows into a table.
● SELECT retrieves data from a table.
● UPDATE modifies data in a table.
● DELETE deletes rows from a table.
The SQL CREATE TABLE statement creates a new table by specifying the table and column names. Each
column is assigned a data type that indicates the format of column values. Data types can be numeric,
textual, or complex. Ex:
● INT stores integer values.
● DECIMAL stores fractional numeric values.
, ● VARCHAR stores textual values.
● DATE stores year, month, and day.
● Analysis
● Logical design
● Physical design
The analysis phase specifies database requirements without regard to a specific database system.
Requirements are represented as entities, relationships, and attributes. An entity is a person, place,
activity, or thing. A relationship is a link between entities, and an attribute is a descriptive property of an
entity.
Analysis has many alternative names, such as conceptual design, entity-relationship modeling, and
requirements definition.
Logical design
The logical design phase implements database requirements in a specific database system. For
relational database systems, logical design converts entities, relationships, and attributes into tables,
keys, and columns.
Physical design
The physical design phase adds indexes and specifies how tables are organized on storage media.
Physical design affects query processing speed but never affects the query result. The principle that
physical design never affects query results is called data independence.
To simplify the use of SQL with a general-purpose language, database programs typically use an
application programming interface. An application programming interface, or API
MySQL Command-Line Client
The MySQL Command-Line Client is a text interface included in the MySQL Server download. MySQL
Server returns an error code and description when an SQL statement is syntactically incorrect or the
database cannot execute the statement.
. A tuple is an ordered collection of elements enclosed in parentheses. Ex: (a, b, c) and (c, b, a) are
different, since tuples are ordered.
The data structure organizes data in tables:
● A table has a name, a fixed tuple of columns, and a varying set of rows.
● A column has a name and a data type.
● A row is an unnamed tuple of values. Each value corresponds to a column and belongs to the
column's data type.
● A data type is a named set of values, from which column values are drawn.
Since a table is a set of rows, the rows have no inherent order.
● Synonyms:
Database Concepts Explained 100% Correct | Graded A+ |
New 2025-2026 Update
A database application is software that helps business users interact with database systems.
Database roles
People interact with databases in a variety of roles:
● A database administrator is responsible for securing the database system against unauthorized
users. A database administrator enforces procedures for user access and database system
availability.
● Authorization. Many database users should have limited access to specific tables, columns, or
rows of a database. Database systems authorize individual users to access specific data.
● Rules. Database systems ensure data is consistent with structural and business rules. Ex: When
multiple copies of data are stored in different locations, copies must be synchronized as data is
updated. Ex: When a course number appears in a student registration record, the course must
exist in the course catalog.
● The query processor interprets queries, creates a plan to modify the database or retrieve data,
and returns query results to the application. The query processor performs query optimization
to ensure the most efficient instructions are executed on the data.
● The storage manager translates the query processor instructions into low-level file-system
commands that modify or retrieve data. Database sizes range from megabytes to many
terabytes, so the storage manager uses indexes to quickly locate data.
● The transaction manager ensures transactions are properly executed. The transaction manager
prevents conflicts between concurrent transactions. The transaction manager also restores the
database to a consistent state in the event of a transaction or system failure.
MongoDB MongoDB NoSQL Open source 5
● INSERT inserts rows into a table.
● SELECT retrieves data from a table.
● UPDATE modifies data in a table.
● DELETE deletes rows from a table.
The SQL CREATE TABLE statement creates a new table by specifying the table and column names. Each
column is assigned a data type that indicates the format of column values. Data types can be numeric,
textual, or complex. Ex:
● INT stores integer values.
● DECIMAL stores fractional numeric values.
, ● VARCHAR stores textual values.
● DATE stores year, month, and day.
● Analysis
● Logical design
● Physical design
The analysis phase specifies database requirements without regard to a specific database system.
Requirements are represented as entities, relationships, and attributes. An entity is a person, place,
activity, or thing. A relationship is a link between entities, and an attribute is a descriptive property of an
entity.
Analysis has many alternative names, such as conceptual design, entity-relationship modeling, and
requirements definition.
Logical design
The logical design phase implements database requirements in a specific database system. For
relational database systems, logical design converts entities, relationships, and attributes into tables,
keys, and columns.
Physical design
The physical design phase adds indexes and specifies how tables are organized on storage media.
Physical design affects query processing speed but never affects the query result. The principle that
physical design never affects query results is called data independence.
To simplify the use of SQL with a general-purpose language, database programs typically use an
application programming interface. An application programming interface, or API
MySQL Command-Line Client
The MySQL Command-Line Client is a text interface included in the MySQL Server download. MySQL
Server returns an error code and description when an SQL statement is syntactically incorrect or the
database cannot execute the statement.
. A tuple is an ordered collection of elements enclosed in parentheses. Ex: (a, b, c) and (c, b, a) are
different, since tuples are ordered.
The data structure organizes data in tables:
● A table has a name, a fixed tuple of columns, and a varying set of rows.
● A column has a name and a data type.
● A row is an unnamed tuple of values. Each value corresponds to a column and belongs to the
column's data type.
● A data type is a named set of values, from which column values are drawn.
Since a table is a set of rows, the rows have no inherent order.
● Synonyms:
