Lesson 6 Flashcards
alias
An alternative name for a column or table in a SQL statement.
ALTER TABLE
- The SQL command used to make changes to table structure.
- When the command is followed by a keyword
ADDorMODIFY, it adds a column or changes column characteristics.
AND
- The SQL logical operator used to link multiple conditional expressions in a
WHEREorHAVINGclause. - It requires that all conditional expressions evaluate to true.
AVG
A SQL aggregate function that outputs the mean average for a specified column or expression.
BETWEEN
In SQL, a special comparison operator used to check whether a value is within a range of specified values.
Boolean algebra
A branch of mathematics that uses the logical operators OR, AND, and NOT.
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.”
COMMIT
The SQL command that permanently writes data changes to a database.
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.
CREATE INDEX
A SQL command that creates indexes on the basis of a selected attribute or attributes.
CREATE TABLE
A SQL command that creates a table’s structures using the characteristics and attributes given.
DELETE
- The
SQL DELETEcommand can delete entire rows from a table. - If you use it with a
WHEREclause, it deletes only the rows matching your condition. - Without a
WHEREclause, it deletes all rows from the table.
DISTINCT
A SQL clause that produces only a list of values that are different from one another.
DROP INDEX
A SQL command that permanently deletes an index.
DROP TABLE
A SQL command that permanently deletes a table and its data.
EXISTS
In SQL, a comparison operator that checks whether a subquery returns any rows.
FROM
A SQL clause that specifies the table or tables from which data is to be retrieved.
GROUP BY
A SQL clause used to create frequency distributions when combined with any of the aggregate functions in a SELECT statement.
HAVING
A clause applied to the output of a GROUP BY operation to restrict selected rows.
IN
In SQL, a comparison operator used to check whether a value is among a list of specified values.
inner query
- A query that is embedded or nested inside another query.
- Also known as a nested query or a subquery.
INSERT
A SQL command that allows the insertion of one or more data rows into a table.
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.
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.
nested query
In SQL, a query that is embedded in another query.
NOT
A SQL logical operator that negates a given predicate.
OR
- The SQL logical operator used to link multiple conditional expressions in a
WHEREorHAVINGclause. - It requires only one of the conditional expressions to be true.
ORDER BY
A SQL clause that is useful for ordering the output of a SELECT query
for example, in ascending or descending order.
ROLLBACK
A SQL command that restores the database table contents to the condition that existed after the last COMMIT statement.
rules of precedence
- Basic algebraic rules that specify the order in which operations are performed.
subquery
A query that is embedded (or nested) inside another query. Also known as a nested query or an inner query.
SUM
A SQL aggregate function that yields the sum of all values for a given column or expression.
