what is a primary key called that is made up of more than one field?

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SQL

SQL - Primary Key, A primary key is a field in a table which uniquely identifies each row/record in a database table. Primary keys must contain unique values. A primary key column

SQL - Primary Key

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A primary key is a field in a table which uniquely identifies each row/record in a database table. Primary keys must contain unique values. A primary key column cannot have NULL values.

A table can have only one primary key, which may consist of single or multiple fields. When multiple fields are used as a primary key, they are called a composite key.

If a table has a primary key defined on any field(s), then you cannot have two records having the same value of that field(s).

Note − You would use these concepts while creating database tables.

Create Primary Key

Here is the syntax to define the ID attribute as a primary key in a CUSTOMERS table.

CREATE TABLE CUSTOMERS(

ID INT NOT NULL,

NAME VARCHAR (20) NOT NULL,

AGE INT NOT NULL,

ADDRESS CHAR (25) ,

SALARY DECIMAL (18, 2),

PRIMARY KEY (ID) );

To create a PRIMARY KEY constraint on the "ID" column when the CUSTOMERS table already exists, use the following SQL syntax −

ALTER TABLE CUSTOMER ADD PRIMARY KEY (ID);

NOTE − If you use the ALTER TABLE statement to add a primary key, the primary key column(s) should have already been declared to not contain NULL values (when the table was first created).

For defining a PRIMARY KEY constraint on multiple columns, use the SQL syntax given below.

CREATE TABLE CUSTOMERS(

ID INT NOT NULL,

NAME VARCHAR (20) NOT NULL,

AGE INT NOT NULL,

ADDRESS CHAR (25) ,

SALARY DECIMAL (18, 2),

PRIMARY KEY (ID, NAME)

);

To create a PRIMARY KEY constraint on the "ID" and "NAMES" columns when CUSTOMERS table already exists, use the following SQL syntax.

ALTER TABLE CUSTOMERS

ADD CONSTRAINT PK_CUSTID PRIMARY KEY (ID, NAME);

Delete Primary Key

You can clear the primary key constraints from the table with the syntax given below.

ALTER TABLE CUSTOMERS DROP PRIMARY KEY ;

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when a primary key combines two or more fields, it is called a ____ key.

Composite Key/Concatenated Key/Multivalued Key. primary key that consists of a combination of fields.

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when a primary key combines two or more fields, it is called a ____ key.

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December 3, 2021 6 minutes read

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Contents

1 When a primary key combines two or more fields it is called?

2 Is a field or combination of fields that uniquely and minimally?

3 Is a field in one table that must match a primary key value in another table in order to establish the relationship between the two tables?

4 Is a graphical model of an information system that depicts the logical relationships?

5 What does PK mean in database?

6 What is a primary key example?

7 Which type of key serves as a field or combination of fields to minimally and uniquely identify a specific instance of an entity?

8 Is a field in a database table or a combination of fields that has a unique value?

9 What is a single fact or piece of information?

10 When a primary key contains more than one field it is known as?

11 Can a table have multiple primary keys?

12 Which key defines relationship between two tables?

13 Which of the following is the advantage of a DBMS database management system )?

14 Is a collection of tools features and interfaces that enables users to add update manage access?

15 What primary key means?

16 What is a primary key Brainly?

17 Why we define primary key?

18 What is a primary key class 10?

19 What is primary key Mcq?

20 What is a primary key quizlet?

21 What is primary key and secondary key?

22 Is primary key a candidate key?

23 What does primary key creates if combined with foreign key?

24 Which key is a field or combination of fields?

25 Can primary key be two columns?

26 Which two types of fields exist in two connected tables?

27 What a single piece of data is called?

28 What is one data called?

29 What do you call a piece of information?

30 What is the relation between primary key and foreign key?

31 What is composite primary key?

32 What is super key and primary key?

33 Can an entity have two primary keys?

34 Can a table have 3 primary keys?

35 Bài 2: [Học SQL từ đầu] – Update table name, column name, data type, primary key, foreign key

36 Primary key on two columns SQL Server

37 SQL-12A: Ràng buộc PRIMARY KEY trong SQL Server.

38 SQL-12B: Ràng buộc PRIMARY KEY vs MySQL.

When a primary key combines two or more fields it is called?

Composite Key/Concatenated Key/Multivalued Key. primary key that consists of a combination of fields.

Is a field or combination of fields that uniquely and minimally?

A field or combination of fields which uniquely identifies every row in a table is known as the key. This is a minimal attribute: if one of the fields is removed from the key, the remaining fields cannot uniquely identify the table rows. Each table must have at least one table key (primary key integrity).

Is a field in one table that must match a primary key value in another table in order to establish the relationship between the two tables?

A secondary key is a field in one table that must match a primary key value in another table in order to establish the relationship between the two tables.

Is a graphical model of an information system that depicts the logical relationships?

An entity relationship diagram (ERD), also known as an entity relationship model, is a graphical representation that depicts relationships among people, objects, places, concepts or events within an information technology (IT) system.

What does PK mean in database?

In the relational model of databases, a primary key is a specific choice of a minimal set of attributes (columns) that uniquely specify a tuple (row) in a relation (table). Informally, a primary key is “which attributes identify a record,” and in simple cases constitute a single attribute: a unique ID.

What is a primary key example?

A primary key is a column — or a group of columns — in a table that uniquely identifies the rows in that table. For example, in the table below, CustomerNo, which displays the ID number assigned to different customers, is the primary key. … In addition, nulls are not allowed in primary key columns.

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Which type of key serves as a field or combination of fields to minimally and uniquely identify a specific instance of an entity?

Emily tells Anna that a primary key is a field or combination of fields that individually and minimally recognizes a specific entity.

Is a field in a database table or a combination of fields that has a unique value?

A field or a combination of fields that has a unique value is called key or foreign key.

What is a single fact or piece of information?

Data Element. A single fact or piece of information. Data Inconsistency.

When a primary key contains more than one field it is known as?

composite key

When multiple fields are used as a primary key, they are called a composite key.

Can a table have multiple primary keys?

Each table can only have one primary key. Access can automatically create a primary key field for you when you create a table, or you can specify the fields that you want to use as the primary key. This article explains how and why to use primary keys. To set a table’s primary key, open the table in Design view.

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In a sophisticated application development software, nulls can create problems when using functions such as:

Select one:

a. COUNT, SUM, and AVERAGE

b. SUM c. COUNT

d. COUNT and AVERAGE

Click card to see definition 👆

a

Click again to see term 👆

A table can be logically connected to another table by defining a ____.

Select one: a. primary key b. common attribute c. hyperlink d. logic key

Click card to see definition 👆

b

Click again to see term 👆

1/15 Created by Kade_Wu

Terms in this set (15)

In a sophisticated application development software, nulls can create problems when using functions such as:

Select one:

a. COUNT, SUM, and AVERAGE

b. SUM c. COUNT

d. COUNT and AVERAGE

a

A table can be logically connected to another table by defining a ____.

Select one: a. primary key b. common attribute c. hyperlink d. logic key b

A relational operator that yields values from all tuples but on selected attributes in a table is known as the ____ operator.

Select one: a. PROJECT b. PRODUCT c. DIFFERENCE d. SELECT a

A relational operator that allows for the combination of information from two or more tables is known as the ____ operator.

Select one: a. DIFFERENCE b. SELECT c. JOIN d. PROJECT c

A primary key that consists of more than one field is called a ____ key.

Select one: a. secondary b. group c. composite d. foreign c

A relational operator that yields all rows in one table that are not found in the other table is the ____ operator.

Select one: a. PRODUCT b. DIFFERENCE c. INTERSECT d. UNION b

Which of the following is NOT an allowable operation for a date field?

Select one:

a. Compare two dates

b. Create a date by adding or subtracting a number of days from a given date

c. Convert a date from its internal representation to a different presentation format

d. Multiply two dates

d

A ____ key is defined as a key that is used strictly for data retrieval purposes.

Select one: a. secondary b. primary c. data d. foreign a

Choose one or more statements that can correctly describe the concept of secondary key.

Select one or more:

a. Primary Key is usually used as a secondary key.

b. Secondary key has to be unique for each row in a table.

c. Secondary key values may be the same for different rows in a table.

d. Secondary key is used for data retrieval purpose.

c,d

What type of value should NOT be represented by NULL in a relational database?

Select one:

a. a known but missing value

b. a 'non applicable' attribute value for the tuple

c. number zero d. an unknown value c

Which of the following is NOT true?

Select one:

a. All foreign key entries must be unique.

b. All primary key entries must be unique.

c. A foreign key entry may have a null value.

d. A non-null foreign key entry must have a value that is the same as one of the primary key values in the table to which it refers.

a

Which of the following is true?

Select one or more:

a. Each table must have at least one attribute that uniquely identifies each row.

b. A primary key has to be a composite key.

c. There could be more than one superkey exist in a relation.

d. A foreign key should not be the primary key of the same table.

e. The order of the rows and columns in a relational table is important for the DBMS.

a,c

Data are classified, according to their format and function, into which categories?

Select one:

a. Numeric and character

b. Numeric and logical

c. Numeric, character, date, and logical

d. Numeric, character, and date

c

According to E.F. Codd, another word for the term "relation" is ____.

Select one: a. data query b. data index c. table d. datafile c

In relational model, a superkey is a key that can uniquely identify ________.

Select one:

a. a dependency in a relation

b. an attribute in a relation

c. a constraint in a relation

d. a tuple in a relation

d

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