What is the primary key, candidate keys, foreign keys, and non-key columns in these two tables? In which normal form is the logical design of the purchases database? **PURCHASE**| Invoice Number | Invoice Date | Pre-Tax Amount | Customer ID ||----------------|--------------|----------------|-------------|| 1 | 2014-05-05 | 155.00 | 1 || 2 | 2014-05-07 | 203.00 | 2 || 3 | 2014-05-11 | 75.00 | 3 || 4 | 2014-05-15 | 67.00 | 4 || 5 | 2014-05-15 | 330.00 | 5 || 6 | 2014-05-16 | 25.00 | 1 || 7 | 2014-05-26 | 45.00 | 3 || 8 | 2014-06-06 | 445.00 | 1 || 9 | 2014-06-07 | 72.00 | 6 |This table records purchase transactions, providing details such as the invoice number, date of purchase, the amount before tax, and the customer ID associated with each transaction. This data can be useful for tracking customer purchasing patterns and understanding sales trends over time. # PURCHASE_ITE Data TableThis table presents a dataset with information about various purchase items, including invoice numbers, line numbers within those invoices, item numbers, and their corresponding retail prices. This data can be used to understand the structure and details of sales transactions.| Invoice Number | Invoice Line Number | Item Number | Retail Price ||----------------|---------------------|-------------|--------------|| 1 | 1 | 1 | 155.00 || 2 | 1 | 2 | 120.00 || 3 | 1 | 3 | 75.00 || 4 | 1 | 6 | 35.00 || 4 | 2 | 7 | 32.00 || 5 | 1 | 4 | 240.00 || 5 | 2 | 8 | 90.00 || 6 | 1 | 10 | 25.00 || 7 | 1 | 11 | 45.00 || 8 | 1 | 5 | 175.00 || 8 | 2 | 9 | 215.00 || 8 | 3 | 12 | 55.00 || 9 | 1 | 14 | 72.00 |### Explanation of Columns:- **Invoice Number**: A unique identifier for each invoice.- **Invoice Line Number**: Indicates the line item within a specific invoice.- **Item Number**: Identifies the specific item purchased.- **Retail Price**: The cost of the item in retail terms.This table is useful in educational settings for exercises related to database management, data analysis, and understanding transaction systems.

Key An attribute, or set of properties, that allows us to specifically identify table rows is known as a key. It also helps to establish relationships between tables. Primary key It is nothing but a column or collection of columns in a table that each individually identifies a row. In DBMS, a primary key is a column or set of columns in a table that uniquely identifies each entry. The same value can not appear more than once in the table than once in the Primary Key, which means it cannot be duplicated. Rules to define the Primary Key: There cannot be duplicate primary key values in two rows. Every row must contain a primary key value. No value can be empty in the primary key field. If any foreign key refers to a primary key column, the value in that column cannot ever be changed or altered. Candidate key It is nothing but a group of characteristics used to distinguish tuples in a table. A super key called the Candidate Key has no repeated characteristics. A set of attributes known as a candidate key in SQL is used to specifically identify tuples in tables. A super key called the Candidate Key has no repeated characteristics. The candidate keys should be chosen to form the primary key. There must be at least one candidate key in each table. There can be several candidate keys but only one primary key in a table. Rules to define the candidate's key It must have distinct values. In SQL, a candidate key could have several attributes. It can not have any empty values Minimum fields should be included to assure uniqueness Create a unique identifier for each table record. Foreign keys It is a column that establishes a connection between two tables. Foreign keys are used to protect data integrity and facilitate communication between two distinct instances of an entity. A column known as a foreign key establishes a connection between two tables. Foreign keys are used to protect data integrity and facilitate communication between two distinct instances of an entity. As it makes reference to another table's primary key, it functions as a cross-reference between two tables. Non-key columns In SQL Server, a non-key attribute is a field that can not be used to uniquely identify a record, such as a name or age column in the customer table. Nonkey columns are columns that are included in a nonclustered index's INCLUDE clause.Primary Key 1. InvoiceNumber - PURCHASE Table In the above-mentioned PURCHASE table, InvoiceNumber is the primary key because it recognizes a particular invoice number. No other customer ID may have the same invoice number in this table. Candidate key 1. InvoiceNumber - PURCHASE Table 2. PreTaxAmount - PURCHASE Table 3. ItemNumber - PURCHASE_ITE Table 4. RetailPrice - PURCHASE_ITE Table In the mentioned table InvoiceNumber, PreTaxAmount, ItemNumber, and RetailPrice are candidate keys that help to uniquely identify the data or record in the table. Foreign keys 1. InvoiceNumber - PURCHASE_ITE Table In the mentioned tables, InvoiceNumber is the foreign key in the PURCHASE_ITE while it is the primary key in the PURCHASE table. Non-key columns Nonkey columns are columns that are included in a nonclustered index's INCLUDE clause. In the above-mentioned tables, No columns are included in the nonclustered index's INCLUDE clause. So, not any non-key columns are present in the PURCHASE, PURCHASE_ITE table. Normal Form In the mentioned table, No multi-valued attributes are present in the purchase database. Hence it will be in 1NF (First Normal Form)