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4.2 KiB
Markdown
187 lines
4.2 KiB
Markdown
# `HAVING` Clause
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Unlike where clause which imposes conditions on columns `Having` clause enables you to specify conditions that filter which group results appear in the results.
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## Syntax
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```sql
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SELECT column_name(s)
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FROM table_name
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WHERE condition
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GROUP BY column_name(s)
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HAVING condition
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ORDER BY column_name(s);
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```
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## Description
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- Used with `aggregate functions`
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- Must follow `GROUP BY` clause in the query
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## Aggregate Functions
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- SQL aggregation is the task of collecting a set of values to return a single value.
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- An aggregate function is a function where the values of multiple rows are grouped together as input on certain criteria to form a single value of more significant meaning.
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## Aggregate Functions Examples
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Suppose this are the table given to us
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|Students | table||
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|--------|-----------|--------|
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| rollno | name | class |
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| 1 | Sanskriti | TE |
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| 1 | Shree | BE |
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| 2 | Harry | TE |
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| 3 | John | TE |
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| 3 | Shivani | TE |
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|purchase | table||
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|------------|-------|---------------|
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| item | price | customer_name |
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| Pen | 10 | Sanskriti |
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| Bag | 1000 | Sanskriti |
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| Vegetables | 500 | Sanskriti |
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| Shoes | 5000 | Sanskriti |
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| Water Bottle | 800 | XYZ |
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| Mouse | 120 | ABC |
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| Sun Glasses | 1350 | ABC |
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### AVG function
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Calculates `average` of the given column of values
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```sql
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SELECT AVG(price) AS Avg_Purchase, customer_name
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FROM purchase
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GROUP BY customer_name;
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```
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| Avg_Purchase | customer_name |
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|--------------|---------------|
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| 1627.5000 | Sanskriti |
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### SUM function
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Calculates `sum` of values of given column.
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```sql
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SELECT SUM(price) AS Total_Bill, customer_name
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FROM purchase
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GROUP BY customer_name;
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```
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| Total_Bill | customer_name |
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|------------|---------------|
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| 6510 | Sanskriti |
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### COUNT function
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Gives `count` of entries/ values in given column.
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```sql
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SELECT COUNT(item) AS Total_Items, customer_name
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FROM purchase
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GROUP BY customer_name;
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```
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| Total_Items | customer_name |
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|-------------|---------------|
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| 4 | Sanskriti |
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### MAX function
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Return `maximum` value from the number of values in the column.
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```sql
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SELECT MAX(price) AS Highest_Purchase, customer_name
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FROM purchase
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GROUP BY customer_name;
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```
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| Highest_Purchase | customer_name |
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|-----------------|---------------|
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| 5000 | Sanskriti |
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### MIN function
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Return `minimum` value from the number of values in the column.
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```sql
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SELECT MIN(price) AS Lowest_Purchase, customer_name
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FROM purchase
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GROUP BY customer_name;
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```
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| Lowest_Purchase | customer_name |
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|-----------------|---------------|
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| 10 | Sanskriti |
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## Having clause Examples
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### Example 1
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```sql
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SELECT COUNT(class) AS strength, class
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FROM Students
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GROUP BY class
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HAVING COUNT(class) > 2;
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```
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Above query gives number of students in a class `having` number of students > 2
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| strength | class |
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|----------|-------|
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| 4 | TE |
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### Example 2
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```sql
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SELECT customer_name, MIN(price) AS MIN_PURCHASE
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FROM purchase
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GROUP BY customer_name
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HAVING MIN(price) > 10;
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```
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Above query finds `minimum` price which is > 10
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| customer_name | MIN_PURCHASE |
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|---------------|------------|
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| XYZ | 800 |
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| ABC | 120 |
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### Example 3
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```sql
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SELECT customer_name, AVG(price) AS Average_Purchase
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FROM purchase
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GROUP BY customer_name
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HAVING AVG(price) > 550
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ORDER BY customer_name DESC;
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```
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Above query calculates `average` of price and prints customer name and average price which is greater than 550 with descending `order` of customer names.
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| customer_name | Average_Purchase |
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|---------------|------------------|
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| XYZ | 800.0000 |
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| Sanskriti | 1627.5000 |
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| ABC | 735.0000 |
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### Example 4
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```sql
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SELECT customer_name, SUM(price) AS Total_Purchase
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FROM purchase
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WHERE customer_name
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LIKE "S%"
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GROUP BY customer_name
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HAVING SUM(price) > 1000;
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```
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Calculates `SUM` of price and returns customer name and sum > 1000.
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| customer_name | Total_Purchase |
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|---------------|----------------|
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| Sanskriti | 6510 |
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