|SQL Server Interview Questions and Answers|
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Please read the Introductory Post before continue reading interview question and answers.
What is the Difference between a Function and a Stored Procedure?
UDF can be used in the SQL statements anywhere in the WHERE/HAVING/SELECT section, whereas Stored procedures cannot be. UDFs that return tables can be treated as another rowset. This can be used in JOINs with other tables. Inline UDF’s can be thought of as views that take parameters and can be used in JOINs and other Rowset operations.
What is subquery? Explain the Properties of a Subquery?
Subqueries are often referred to as sub-selects as they allow a SELECT statement to be executed arbitrarily within the body of another SQL statement. A subquery is executed by enclosing it in a set of parentheses. Subqueries are generally used to return a single row as an atomic value although they may be used to compare values against multiple rows with the IN keyword.
A subquery is a SELECT statement that is nested within another T-SQL statement. A subquery SELECT statement if executed independently of the T-SQL statement, in which it is nested, will return a resultset. This implies that a subquery SELECT statement can stand alone, and it does not depend on the statement in which it is nested. A subquery SELECT statement can return any number of values and can be found in the column list of a SELECT statement, and FROM, GROUP BY, HAVING, and/or ORDER BY clauses of a T-SQL statement. A subquery can also be used as a parameter to a function call. Basically, a subquery can be used anywhere an expression can be used. (Read more here)
What are Different Types of Join?
A cross join that does not have a WHERE clause produces the Cartesian product of the tables involved in the join. The size of a Cartesian product result set is the number of rows in the first table multiplied by the number of rows in the second table. The common example is when company wants to combine each product with a pricing table to analyze each product at each price.
A join that displays only the rows that have a match in both joined tables is known as inner Join. This is the default type of join in the Query and View Designer.
A join that includes rows even if they do not have related rows in the joined table is an Outer Join. You can create three different outer join to specify the unmatched rows to be included:
- Left Outer Join: In Left Outer Join, all the rows in the first-named table, i.e. “left” table, which appears leftmost in the JOIN clause, are included. Unmatched rows in the right table do not appear.
- Right Outer Join: In Right Outer Join, all the rows in the second-named table, i.e. “right” table, which appears rightmost in the JOIN clause are included. Unmatched rows in the left table are not included.
- Full Outer Join: In Full Outer Join, all the rows in all joined tables are included, whether they are matched or not.
This is a particular case when one table joins to itself with one or two aliases to avoid confusion. A self join can be of any type, as long as the joined tables are the same. A self join is rather unique in that it involves a relationship with only one table. The common example is when company has a hierarchal reporting structure whereby one member of staff reports to another. Self Join can be Outer Join or Inner Join. (Read more here)
What are Primary Keys and Foreign Keys?
Primary keys are the unique identifiers for each row. They must contain unique values and cannot be null. Due to their importance in relational databases, Primary keys are the most fundamental aspect of all keys and constraints. A table can have only one primary key.
Foreign keys are a method of ensuring data integrity and manifestation of the relationship between tables.
What is User-defined Functions? What are the types of User-defined Functions that can be created?
User-defined Functions allow defining its own T-SQL functions that can accept zero or more parameters and return a single scalar data value or a table data type.
Different Types of User-Defined Functions created are as follows:
Scalar User-defined Function
A scalar user-defined function returns one of the scalar data types. Text, ntext, image and timestamp data types are not supported. These are the type of user-defined functions that most developers are used to in other programming languages.
Inline Table-Value User-defined Function
An Inline table-value user-defined function returns a table data type and is an exceptional alternative to a view as the user-defined function can pass parameters into a T-SQL select command and in essence provide us with a parameterized, non-updateable view of the underlying tables.
Multi-Statement Table-Value User-defined Function
A multi-statement table-value user-defined function returns a table, and it is also an exceptional alternative to a view as the function can support multiple T-SQL statements to build the final result where the view is limited to a single SELECT statement. Also, the ability to pass parameters into a T-SQL select command or a group of them gives us the capability to in essence create a parameterized, non-updateable view of the data in the underlying tables. Within the create function command, you must define the table structure that is being returned. After creating this type of user-defined function, It can be used in the FROM clause of a T-SQL command unlike the behavior encountered while using a stored procedure which can also return record sets. (Read here for example)
Reference: Pinal Dave (http://blog.SQLAuthority.com)