SQL window functions Tutorial (9)

SQL window functions Tutorial (9)

SQL window Functions

What is Scalar Functions in SQL?

 In SQL, a scalar function is a type of function that operates on a single value and returns a single value. It is typically used to perform computations on input values and generate a result.

Scalar functions can be used in various SQL statements, such as SELECT, WHERE, and ORDER BY, to manipulate data during retrieval or to perform calculations within queries.

These functions can be built-in functions provided by the database management system (DBMS) or user-defined functions created by users to fulfill specific requirements.

Some common examples of scalar functions in SQL include:

String functions: Functions that operate on string values, such as LEN, UPPER, LOWER, SUBSTRING, and CONCAT.

Numeric functions: Functions that operate on numeric values, such as ROUND, CEILING, FLOOR, and ABS.

Date and time functions: Functions that handle date and time values, such as GETDATE, DATEPART, and DATEADD.

Conversion functions: Functions that convert data from one type to another, such as CAST and CONVERT.

Aggregate functions used in a scalar context: These include functions like SUM, AVG, MIN, and MAX when used with a GROUP BY clause to return a single value for each group.

Scalar functions are beneficial for simplifying complex operations, performing data manipulations, and generating computed values during result retrieval. However, their use should be considered carefully as they can impact query performance, particularly when applied to large datasets.

Introduction-Scalar Functions

 Scalar functions in SQL are used to perform operations on individual values in a database. These functions operate on each row of a query result and return a single value. They can be either built-in functions provided by the database management system or user-defined functions created to cater to specific needs.

 Commonly used scalar functions include those for manipulating strings, numbers, dates, and conversions between different data types.

For instance, string functions may include operations like changing the case of a string, extracting substrings, or concatenating multiple strings. Numeric functions often involve rounding, finding absolute values, or performing mathematical calculations.

Date and time functions facilitate operations on date and time values, such as extracting parts of a date or adding/subtracting intervals. Conversion functions, on the other hand, allow data type conversions between different formats.

 When using scalar functions, it is important to consider their impact on the performance of the SQL query, especially when dealing with large datasets.

Overuse of scalar functions can potentially slow down query execution, so it is crucial to use them judiciously and optimize their usage wherever possible. Understanding how scalar functions can streamline complex operations and simplify data manipulations is essential for efficient and effective database management.

String Functions in SQL?

String functions in SQL are used to manipulate character or text data. They allow for operations such as concatenation, extraction, searching, and modification of strings. Here are some common string functions in SQL:

CONCAT: Used to concatenate two or more strings together.

Example:

SELECT CONCAT(‘Hello’, ‘ ‘, ‘World’) AS ConcatenatedString;

Output:

ConcatenatedString

—————–

Hello World

ConcatenatedString

—————–

Hello World

UPPER: Converts all characters in a string to uppercase.

Example:

SELECT UPPER(‘hello’) AS UppercaseString;

Output:

UppercaseString

—————

HELLO

LOWER: Converts all characters in a string to lowercase.

Example:

SELECT LOWER(‘HELLO’) AS LowercaseString;

Output:

LowercaseString

—————

Hello

SUBSTRING: Extracts a substring from a string based on a specified starting position and length.

Example:

SELECT SUBSTRING(‘Hello World’, 7, 5) AS ExtractedString;

Output:

ExtractedString

—————

World

LEN (or LENGTH): Returns the length of a string.

Example:

SELECT LEN(‘Hello’) AS StringLength;

Output:

StringLength

————

5

LTRIM and RTRIM: Remove leading and trailing spaces from a string, respectively.

Example:

SELECT LTRIM(‘   Hello’) AS LeftTrimmedString;

SELECT RTRIM(‘World   ‘) AS RightTrimmedString;

Output:

LeftTrimmedString

—————–

Hello

RightTrimmedString

——————

World

These functions can be used within SELECT statements, WHERE clauses, or as part of data manipulation operations to process and transform string data as needed. They are particularly useful for tasks involving data cleansing, formatting, and analysis.

Numeric Functions in SQL?

Numeric functions in SQL are used to perform operations on numeric data types. These functions are helpful in performing various mathematical calculations, rounding numbers, and obtaining specific numeric values. Some commonly used numeric functions in SQL include the following:

ROUND: Rounds a numeric value to a specified precision.

Example:

SELECT ROUND(15.67) AS RoundedValue;

Output:

RoundedValue

————

16

CEILING: Rounds a numeric value up to the nearest integer.

Example:

SELECT CEILING(15.25) AS CeilingValue;

Output:

CeilingValue

————

16

FLOOR: Rounds a numeric value down to the nearest integer.

Example:

SELECT FLOOR(15.75) AS FloorValue;

Output:

FloorValue

———-

15

ABS: Returns the absolute value of a numeric expression.

Example:

SELECT ABS(-15) AS AbsoluteValue;

Output:

AbsoluteValue

————-

15

How to Using the CASE Statement in SQL with Example

The CASE statement in SQL is a conditional statement that allows you to perform different actions based on different conditions.

It can be used in various ways, including comparing values, evaluating conditions, and returning specific values based on the comparison results. Here is an example of how to use the CASE statement in SQL:

Suppose we have a table called Students with the following data:

StudentIDNameAge
1John20
2Sarah18
3Michael22
4JessicaNULL

We want to create a query that returns a result indicating whether the student is a minor or an adult based on their age. Here’s how you can use the CASE statement for this:

SELECT

    StudentID,

    Name,

    Age,

    CASE

        WHEN Age < 18 THEN ‘Minor’

        WHEN Age >= 18 THEN ‘Adult’

        ELSE ‘Age not specified’

    END AS AgeGroup

FROM Students;

In this example, the CASE statement checks the value of the Age column for each row. If the age is less than 18, it returns ‘Minor’. If the age is 18 or greater, it returns ‘Adult’.

If the age is NULL or not specified, it returns ‘Age not specified’. The result set will include the student ID, name, age, and the corresponding age group for each student.

The Output of the Query will be:
StudentIDNameAgeAgeGroup
1John20Adult
2Sarah18Adult
3Michael22Adult
4JessicaNULLAge not specified

The CASE statement is versatile and can be used in various scenarios to perform conditional operations, manipulate data, and create customized result sets based on specific conditions.

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