SQL | Functions (Aggregate and Scalar Functions)

For doing operations on data sql has many built-in functions, they are categorised in two categories and further sub-categorised in different seven functions under each category. The categories are:

1. Aggregate functions:
These functions are used to do operations from the values of the column and a single value is returned.

1. AVG()
2. COUNT()
3. FIRST()
4. LAST()
5. MAX()
6. MIN()
7. SUM()
2. Scalar functions:
These functions are based on user input, these too returns single value.

1. UCASE()
2. LCASE()
3. MID()
4. LEN()
5. ROUND()
6. NOW()
7. FORMAT()

Students-Table

Aggregate Functions

• AVG(): It returns average value after calculating from values in a numeric column.
Syntax:

```SELECT AVG(column_name) FROM table_name;
```

Queries:

1. Computing average marks of students.
```SELECT AVG(MARKS) AS AvgMarks FROM Students;
```

Output:

 AvgMarks 80
2. Computing average age of students.
```SELECT AVG(AGE) AS AvgAge FROM Students;
```

Output:

 AvgAge 19.4
• COUNT(): It is used to count the number of rows returned in a SELECT statement. It can’t be used in MS ACCESS.
Syntax:

```SELECT COUNT(column_name) FROM table_name;
```

Queries:

1. Computing total number of students.
```SELECT COUNT(*) AS NumStudents FROM Stuents;
```

Output:

 NumStudents 5
2. Computing number of students with unique/distinct age.
```SELECT COUNT(DISTINCT AGE) AS NumStudents FROM Students;
```

Output:

 NumStudents 4
• FIRST(): The FIRST() function returns the first value of the selected column.
Syntax:

```SELECT FIRST(column_name) FROM table_name;
```

Queries:

1. Fetching marks of first student from the Students table.
```SELECT FIRST(MARKS) AS MarksFirst FROM Students;
```

Output:

 MarksFirst 90
2. Fetching age of first student from the Students table.
```SELECT FIRST(AGE) AS AgeFirst FROM Students;
```

Output:

 AgeFirst 19
• LAST(): The LAST() function returns the last value of the selected column. It can be used only in MS ACCESS.
Syntax:

```SELECT LAST(column_name) FROM table_name;
```

Queries:

1. Fetching marks of last student from the Students table.
```SELECT LAST(MARKS) AS MarksLast FROM Students;
```

Output:

 MarksLast 82
2. Fetching age of last student from the Students table.
```SELECT FIRST(AGE) AS AgeLast FROM Students;
```

Output:

 AgeLast 18
• MAX(): The MAX() function returns the maximum value of the selected column.
Syntax:

```SELECT MAX(column_name) FROM table_name;
```

Queries:

1. Fetching maximum marks among students from the Students table.
```SELECT MAX(MARKS) AS MaxMarks FROM Students;
```

Output:

 MaxMarks 95
2. Fetching max age among students from the Students table.
```SELECT MAX(AGE) AS MaxAge FROM Students;
```

Output:

 MaxAge 21
• MIN(): The MIN() function returns the minimum value of the selected column.
Syntax:

```SELECT MIN(column_name) FROM table_name;
```

Queries:

1. Fetching minimum marks among students from the Students table.
```SELECT MIN(MARKS) AS MinMarks FROM Students;
```

Output:

 MinMarks 50
2. Fetching minimum age among students from the Students table.
```SELECT MIN(AGE) AS MinAge FROM Students;
```

Output:

 MinAge 18
• SUM(): The SUM() function returns the sum of all the values of the selected column.
Syntax:

```SELECT SUM(column_name) FROM table_name;
```

Queries:

1. Fetching summation of total marks among students from the Students table.
```SELECT SUM(MARKS) AS TotalMarks FROM Students;
```

Output:

 TotalMarks 400
2. Fetching summation of total age among students from the Students table.
```SELECT SUM(AGE) AS TotalAge FROM Students;
```

Output:

 TotalAge 97

Scalar Functions

• UCASE(): It converts the value of a field to uppercase.
Syntax:

```SELECT UCASE(column_name) FROM table_name;
```

Queries:

1. Converting names of students from the table Students to uppercase.
```SELECT UCASE(NAME) FROM Students;
```

Output:

 NAME HARSH SURESH PRATIK DHANRAJ RAM
• LCASE(): It converts the value of a field to lowercase.
Syntax:

```SELECT LCASE(column_name) FROM table_name;
```

Queries:

1. Converting names of students from the table Students to lowercase.
```SELECT LCASE(NAME) FROM Students;
```

Output:

 NAME harsh suresh pratik dhanraj ram
• MID(): The MID() function extracts texts from the text field.
Syntax:

```SELECT MID(column_name,start,length) AS some_name FROM table_name;

specifying length is optional here, and start signifies start position ( starting from 1 )
```

Queries:

1. Fetching first four characters of names of students from the Students table.
```SELECT MID(NAME,1,4) FROM Students;
```

Output:

 NAME HARS SURE PRAT DHAN RAM
• LEN(): The LEN() function returns the length of the value in a text field.
Syntax:

```SELECT LENGTH(column_name) FROM table_name;
```

Queries:

1. Fetching length of names of students from Students table.
```SELECT LENGTH(NAME) FROM Students;
```

Output:

 NAME 5 6 6 7 3
• ROUND(): The ROUND() function is used to round a numeric field to the number of decimals specified.NOTE: Many database systems have adopted the IEEE 754 standard for arithmetic operations, which says that when any numeric .5 is rounded it results to the nearest even integer i.e, 5.5 and 6.5 both gets rounded off to 6.

Syntax:

```SELECT ROUND(column_name,decimals) FROM table_name;

decimals- number of decimals to be fetched.
```

Queries:

1. Fetching maximum marks among students from the Students table.
```SELECT ROUND(MARKS,0) FROM table_name;
```

Output:

 MARKS 90 50 80 95 85
• NOW(): The NOW() function returns the current system date and time.
Syntax:

```SELECT NOW() FROM table_name;
```

Queries:

1. Fetching current system time.
```SELECT NAME, NOW() AS DateTime FROM Students;
```

Output:

 NAME DateTime HARSH 1/13/2017 1:30:11 PM SURESH 1/13/2017 1:30:11 PM PRATIK 1/13/2017 1:30:11 PM DHANRAJ 1/13/2017 1:30:11 PM RAM 1/13/2017 1:30:11 PM
• FORMAT(): The FORMAT() function is used to format how a field is to be displayed.
Syntax:

```SELECT FORMAT(column_name,format) FROM table_name;
```

Queries:

1. Formatting current date as ‘YYYY-MM-DD’.
```SELECT NAME, FORMAT(Now(),'YYYY-MM-DD') AS Date FROM Students;
```

Output:

 NAME Date HARSH 2017-01-13 SURESH 2017-01-13 PRATIK 2017-01-13 DHANRAJ 2017-01-13 RAM 2017-01-13