Database Systems - Chapter 7 Glossary

COMMIT

The SQL command that permanently saves data changes to a database.

ALTER TABLE

The SQL command used to make changes to table structure. When the command is followed by a keyword (ADD or MODIFY), it adds a column or changes column characteristics.

authentication

The SQL command used to make changes to table structure. When the command is followed by a keyword (ADD or MODIFY), it adds a column or changes column characteristics.

OR

The SQL logical operator used to link multiple conditional expressions in a WHERE or HAVING clause. It requires only one of the conditional expressions to be true.

AND

The SQL logical operator used to link multiple conditional expressions in a WHERE or HAVING clause. It requires that all conditional expressions evaluate to true.

UPDATE

A SQL command that allows attribute values to be changed in one or more rows of a table.

DELETE

A SQL command that allows data rows to be deleted from a table.

INSERT

A SQL command that allows the insertion of one or more data rows into a table using a subquery.

CREATE VIEW

A SQL command that creates a logical, "virtual" table based on stored end-user tables. The view can be treated as a real table.

CREATE TABLE

A SQL command that creates a table's structures using the characteristics and attributes given.

CREATE INDEX

A SQL command that creates indexes on the basis of a selected attribute or attributes.

ROLLBACK

A SQL command that restores the database table contents to the condition that existed after the last COMMIT statement.

SELECT

A SQL command that yields the values of all rows or a subset of rows in a table. The SELECT statement is used to retrieve data from tables.

DROP INDEX

A SQL commands that deletes indexes

DROP TABLE

A SQL commands that deletes tables.A SQL commands that deletes indexes. You can drop a table only if it is not the "one" side of any relationship. If you try to drop a table otherwise, the RDBMS will generate an error message indicating that a foreign key integrity violation has occurred.

NOT

A SQL logical operator that negates a given predicate.

Boolean algebra

A branch of mathematics that uses the logical operators OR, AND, and NOT.

HAVING

A clause applied to the output of a GROUP BY operation to restrict selected rows.

schema

A logical grouping of database objects, such as tables, indexes, views, and queries, that are related to each other. Usually, a schema belongs to a single user or application.

cascading order sequence

A nested ordering sequence for a set of rows, such as a list in which all last names are alphabetically ordered and, within the last names, all first names are ordered.

recursive query

A nested query that joins a table to itself.

subquery

A query that is embedded (or nested) inside another query. Also known as a nested query or an inner query.

inner query

A query that is embedded or nested inside another query. Also known as a nested query or a subquery.

wildcard character

A symbol that can be used as a general substitute for one or more characters in a SQL LIKE clause condition. The wildcard characters used in SQL are the _ and % symbols.

rules of precedence

Basic algebraic rules that specify the order in which operations are performed. For example, operations within parentheses are executed first, so in the equation 2 + (3 × 5), the multiplication portion is calculated first, making the correct answer 17.

EXISTS

In SQL, a comparison operator that checks whether a subquery returns any rows.

IN

In SQL, a comparison operator used to check whether a value is among a list of specified values.

IS NULL

In SQL, a comparison operator used to check whether an attribute has a value.

LIKE

In SQL, a comparison operator used to check whether an attribute's text value matches a specified string pattern.

nested query

In SQL, a query that is embedded in another query. See subquery.

BETWEEN

In SQL, a special comparison operator used to check whether a value is within a range of specified values.

alias

An alternative name for a column or table in a SQL statement.

AVG

A SQL aggregate function that outputs the mean average for a specified column or expression.

COUNT

A SQL aggregate function that outputs the number of rows containing not null values for a given column or expression, sometimes used in conjunction with the DISTINCT clause.

MAX

A SQL aggregate function that yields the maximum attribute value in a given column.

MIN

A SQL aggregate function that yields the minimum attribute value in a given column.

SUM

A SQL aggregate function that yields the sum of all values for a given column or expression.

ORDER BY

A SQL clause that is useful for ordering the output of a SELECT query (for example, in ascending or descending order).

DISTINCT

A SQL clause that produces only a list of values that are different from one another.

GROUP BY

A SQL clause used to create frequency distributions when combined with any of the aggregate functions in a SELECT statement.

reserved words

Words used by a system that cannot be used for any other purpose. For example, in Oracle SQL, the word INITIAL cannot be used to name tables or columns.