SQL HAVING clause is used with aggregate functions.

Syntaxt

SELECT column_name, aggregate_function(column_name)
FROM table_name
GROUP BY column_name
HAVING aggregate_function(column_name) operator value

Table – Users

+—–+——+
| uid | name |
+—–+——+
|   1 | AAAA |
|   2 | BBBB |
|   3 | CCCC |
|   4 | DDDD |
|   5 | EEEE |
+—–+——+

Table – Orders

+—–+—–+——-+
| oid | uid | price |
+—–+—–+——-+
|   1 |   1 | 60    |
|   2 |   2 | 30    |
|   3 |   2 | 60    |
|   4 |   1 | 70    |
|   5 |   2 | 80    |
|   6 |   1 | 50    |
+—–+—–+——-+

Example

mysql> SELECT SUM(o.price) AS total,u.name FROM users AS u JOIN orders AS o ON u.uid=o.uid GROUP BY o.uid HAVING total >175;
+——-+——+
| total | name |
+——-+——+
|   180 | AAAA |
+——-+——+
1 row in set (0.00 sec)

SQL GROUP BY should be added with all aggregate functions and it s used in conjunction with the aggregate functions to group the result-set by one or more columns.

Table – Users

+—–+——+
| uid | name |
+—–+——+
|   1 | AAAA |
|   2 | BBBB |
|   3 | CCCC |
|   4 | DDDD |
|   5 | EEEE |
+—–+——+

Table – Orders

+—–+—–+——-+
| oid | uid | price |
+—–+—–+——-+
|   1 |   1 | 60    |
|   2 |   2 | 30    |
|   3 |   2 | 60    |
|   4 |   1 | 70    |
|   5 |   2 | 80    |
|   6 |   1 | 50    |
+—–+—–+——-+

Example

mysql> SELECT SUM(o.price) AS total,u.name FROM users AS u JOIN orders AS o ON u.uid=o.uid GROUP BY o.uid;;
+——-+——+
| total | name |
+——-+——+
| 180 | AAAA |
| 170 | BBBB |
+——-+——+
2 rows in set (0.00 sec)

SQL SUM()  returns the total sum of a numeric column.

Table – Students

+—–+——+——-+——-+——-+
| sid | name | mark1 | mark2 | mark3 |
+—–+——+——-+——-+——-+
|   1 | AAAA |    30 |    35 |    40 |
|   2 | BBBB |    36 |    37 |    38 |
|   3 | CCCC |    42 |    43 |    44 |
|   4 | DDDD |    43 |    32 |    39 |
+—–+——+——-+——-+——-+

Example

mysql> SELECT SUM(mark1) FROM students ;
+————+
| SUM(mark1) |
+————+
|        151 |
+————+
1 row in set (0.00 sec)

SQL MIN()  returns the smallest value of the selected column.

Table – Students

+—–+——+——-+——-+——-+
| sid | name | mark1 | mark2 | mark3 |
+—–+——+——-+——-+——-+
|   1 | AAAA |    30 |    35 |    40 |
|   2 | BBBB |    36 |    37 |    38 |
|   3 | CCCC |    42 |    43 |    44 |
|   4 | DDDD |    43 |    32 |    39 |
+—–+——+——-+——-+——-+

Example

mysql> SELECT MIN(mark1) FROM students ;
+————+
| MIN(mark1) |
+————+
|         30 |
+————+
1 row in set (0.00 sec)

SQL MAX()  returns the largest value of the selected column.

Table – Students

+—–+——+——-+——-+——-+
| sid | name | mark1 | mark2 | mark3 |
+—–+——+——-+——-+——-+
|   1 | AAAA |    30 |    35 |    40 |
|   2 | BBBB |    36 |    37 |    38 |
|   3 | CCCC |    42 |    43 |    44 |
|   4 | DDDD |    43 |    32 |    39 |
+—–+——+——-+——-+——-+

Example

mysql> SELECT MAX(mark1) FROM students ;
+————+
| MAX(mark1) |
+————+
|         43 |
+————+
1 row in set (0.00 sec)

SQL LAST() returns the last value of the selected column.

Table – Students

+—–+——+——-+——-+——-+
| sid | name | mark1 | mark2 | mark3 |
+—–+——+——-+——-+——-+
|   1 | AAAA |    30 |    35 |    40 |
|   2 | BBBB |    36 |    37 |    38 |
|   3 | CCCC |    42 |    43 |    44 |
|   4 | DDDD |    43 |    32 |    39 |
+—–+——+——-+——-+——-+

Example

SELECT LAST(*) AS total FROM students ;

SQL FIRST() returns the first value of the selected column.

Table – Students

+—–+——+——-+——-+——-+
| sid | name | mark1 | mark2 | mark3 |
+—–+——+——-+——-+——-+
|   1 | AAAA |    30 |    35 |    40 |
|   2 | BBBB |    36 |    37 |    38 |
|   3 | CCCC |    42 |    43 |    44 |
|   4 | DDDD |    43 |    32 |    39 |
+—–+——+——-+——-+——-+

Example

SELECT FIRST(*) AS total FROM students ;

SQL COUNT() returns the number of rows

Table – Students

+—–+——+——-+——-+——-+
| sid | name | mark1 | mark2 | mark3 |
+—–+——+——-+——-+——-+
|   1 | AAAA |    30 |    35 |    40 |
|   2 | BBBB |    36 |    37 |    38 |
|   3 | CCCC |    42 |    43 |    44 |
|   4 | DDDD |    43 |    32 |    39 |
+—–+——+——-+——-+——-+

Example

mysql> SELECT COUNT(*) AS total FROM students ;
+——-+
| total |
+——-+
|     4 |
+——-+
1 row in set (0.01 sec)

SQL AVG() function returns the average value of a numeric column.

Table – Students
+—–+——+——-+——-+——-+
| sid | name | mark1 | mark2 | mark3 |
+—–+——+——-+——-+——-+
|   1 | AAAA |    30 |    35 |    40 |
|   2 | BBBB |    36 |    37 |    38 |
|   3 | CCCC |    42 |    43 |    44 |
|   4 | DDDD |    43 |    32 |    39 |
+—–+——+——-+——-+——-+

Example

mysql> SELECT AVG(mark1) FROM students ;
+————+
| AVG(mark1) |
+————+
|    37.7500 |
+————+
1 row in set (0.02 sec)

Below given the SQL functions

• SQL NOW()– Returns the current date and time
• SQL CURDATE()– Returns the current date
• SQL CURTIME()– Returns the current time
• SQL DATE()– Extracts the date part of a date or date/time expression
• SQL EXTRACT()- Returns a single part of a date/time
• SQL DATE_ADD()– Adds a specified time interval to a date
• SQL DATE_SUB() -Subtracts a specified time interval from a date
• SQL DATEDIFF()– Returns the number of days between two dates
• SQL DATE_FORMAT()– Displays date/time data in different formats
• SQL NULL Functions – We can use these function to manage the null values
• SQL avg() – returns the average value of a numeric column
• SQL count() –  returns the number of rows
• SQL first() –  returns the first value of the selected column.
• SQL last() –  returns the last value of the selected column.
• SQL max() – returns the largest value of the selected column.
• SQL min() –  returns the smallest value of the selected column.
• SQL sum() – returns the total sum of a numeric column.
• SQL Group By – should be added with all aggregate functions
• SQL ucase() –   converts the value of a field to uppercase.
• SQL lcase() –  converts the value of a field to lowercase.
• SQL mid() –  used to extract characters from a text field
• SQL len() – returns the length of the value in a text field.
• SQL round() –  used to round a numeric field to the number of decimals specified.