Understanding Questions For SQL Server & SQL Server Management Studio Part II


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.


Explain What is a Identity Column ?

  • Identity column of a table is a column whose value increases automatically. 

  • The value in an identity column is created by the server. 

  • A user generally cannot insert a value into an identity column.

  • Identity column can be used to uniquely identify the rows in the table.


How can I create One to Many relationship ?

  • In a one-to-many relationship, one record in a table can be associated with one or more records in another table.

How can I create Primary Key & Foreign Key relationship ?

  • In a foreign key reference, a link is created between two tables when the column or columns that hold the primary key value for one table are referenced by the column or columns in another table. 

  • This column becomes a foreign key in the second table.


Are NULLs allowed in Foreign Key ?

  • Yes, it can be NULL. 

  • A Foreign key simply requires that the value in that field must exist first in a different table. 

  • Null by definition is not a value.


How can we create Composite Key ?

  • Composite key is a key which is the combination of more than one field or column of a given table.


How to write a simple SQL with Where Clause ?

  • The WHERE clause is used to filter records.

  • It is used to extract only those records that fulfill a specified condition.

How to Select specific Column in Select ?

  • The column names that follow the select keyword determine which columns will be returned in the results.


What is an ALIAS in SQL ?

  • SQL aliases are used to give a temporary name.

  • An alias is created with the AS keyword.


Explain the Difference between Inner vs Left vs Right ?

  • INNER JOIN : Returns records that have matching values in both tables.

  • LEFT JOIN : Returns all records from the left table, and the matched records from the right table.

  • RIGHT JOIN : Returns all records from the right table, and the matched records from the left table.

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