SQL Data Definition and Data Types

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Questions and Answers

What distinguishes base tables from virtual relations in SQL?

Virtual relations are created using manual inputs; base tables do not allow this.

Base tables store data physically, whereas virtual relations do not store data directly. (correct)

Base tables can only contain numeric data, while virtual relations can contain any data type.

Base tables are temporary tables, while virtual relations are permanent.

Which of the following character-string data types can hold varying lengths of strings?

CHAR(n)

FIXEDCHAR(n)

VARCHAR(n) (correct)

CHARACTER(n)

Which SQL data type is used to store a value that can either be TRUE, FALSE, or NULL?

REAL

INTEGER

BOOLEAN (correct)

CHAR(n)

What is a distinguishing feature of the TIMESTAMP data type in SQL?

It includes both DATE and TIME fields with added precision. Signup and view all the answers

Which numeric data type in SQL is best suited for storing very large floating-point numbers?

DOUBLE PRECISION Signup and view all the answers

What does SQL stand for?

Structured Query Language Signup and view all the answers

Which SQL command is primarily used for data definition?

CREATE Signup and view all the answers

What is a schema in SQL?

A named collection of database objects Signup and view all the answers

Which of the following elements is NOT part of an SQL schema?

Procedures Signup and view all the answers

What punctuation must every SQL statement end with?

; Signup and view all the answers

Which SQL command is used to create a new table?

CREATE TABLE Signup and view all the answers

In SQL, the command to specify an authorization identifier in a schema is called what?

CREATE SCHEMA Signup and view all the answers

Which of the following statements about SQL is true?

SQL supports both data definition and data manipulation. Signup and view all the answers

What is the purpose of the INTERVAL data type in SQL?

To represent a relative value for date, time, or timestamp adjustments. Signup and view all the answers

Which statement accurately describes the role of a domain in SQL?

They improve schema readability by allowing attribute type changes in one place. Signup and view all the answers

What does the PRIMARY KEY clause specify in SQL?

A unique identifier for a relation's records. Signup and view all the answers

What action occurs by default when a foreign key constraint is violated?

The operation is rejected and no changes are made. Signup and view all the answers

Which of the following accurately describes a CHECK clause?

It applies individual conditions to each tuple during table creation. Signup and view all the answers

What does the NOT NULL constraint do in SQL?

It prevents NULL values from being entered for an attribute. Signup and view all the answers

What is specified by using the UNIQUE clause in SQL?

It identifies attributes that should contain unique values. Signup and view all the answers

How can constraints in SQL be named effectively?

By using the keyword CONSTRAINT to provide a specific name. Signup and view all the answers

In which scenario would a circular reference error occur regarding foreign keys?

When a foreign key is defined but the corresponding table does not exist. Signup and view all the answers

Study Notes

SQL Data Definition and Data Types

Terminology used: table, row, and column
SQL uses the CREATE statement for data definition.
SQL Schema is identified by a schema name.
Schema elements include: tables, constraints, views, domains, and other constructs.
Each SQL statement ends with a semicolon.
The CREATE SCHEMA statement is used to create a new schema for an SQL database.
A catalog is a named collection of schemas in an SQL environment.
CREATE TABLE specifies a new relation with a name, attributes, and initial constraints.
Base tables are actually created and stored as files by the DBMS.
Virtual relations are created using the CREATE VIEW statement.
Basic data types include: integer, floating-point, character-string, bit-string, boolean, and date.
Additional data types include: timestamp, interval.
CHAR(N) and VARCHAR(N) are used to specify character-string data types.
Domain is a name used with the attribute specification for easier data type changes and improved readability.

Specifying Constraints in SQL

Basic constraints include: key and referential integrity constraints, restrictions on attribute domains and NULLs, and constraints on individual tuples within a relation.
NOT NULL enforces that NULL is not allowed for an attribute.
DEFAULT specifies a default value for an attribute.
CHECK clause verifies that a condition is met.
Dnumber INT NOT NULL CHECK (Dnumber > 0 AND Dnumber < 21); constrains Dnumber to be an integer greater than zero and less than 21, and does not allow NULL values.
PRIMARY KEY clause specifies the primary key of the relation.
UNIQUE clause specifies alternate or secondary keys.
FOREIGN KEY clause specifies referential integrity constraints.
Default operation: reject update on violation of constraints.
FOREIGN KEY clause can have additional triggered actions: SET NULL, CASCADE, SET DEFAULT.
The CASCADE option is suitable for "relationship" relations.
The CONSTRAINT keyword can be used to name constraints allowing for easier alteration later.
CHECK clauses at the end of a CREATE TABLE statement apply to individual tuples.
CHECKclauses can be used to enforce constraints on data within a relation
CHECK (Dept_create_date < CURRENT_DATE)
- This ensures that the department creation date is always before the current date.

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Description

This quiz covers the essential terminology and concepts related to SQL data definition and data types. It includes topics such as the CREATE statement, SQL schema elements, basic and additional data types, and their specifications. Test your understanding of these fundamental aspects of SQL databases.