Restricting group results

Introduzione a Oracle SQL

Hadrien Lacroix

Content Developer

Back to our example

SELECT Composer, AVG(Milliseconds)
FROM Track
WHERE UnitPrice = 0.99
GROUP BY Composer

| Composer        | AVG(Milliseconds) |
|-----------------|-------------------|
| Antonio Vivaldi | 199,086.0         |
| Pearl Jam       | 94,197.0          |
| Jimmy Page      | 474,888.3         |
| Carlos Santana  | 499,234.3         |
| ...             | ...               |

What about filtering after grouping?

Limits of WHERE

WHERE can't be used to filter groups
- Group functions can't be used in WHERE clauses

Limits of WHERE example

SELECT Composer, AVG(Milliseconds)
FROM Track
GROUP BY Composer
WHERE AVG(Milliseconds) > 200000

syntax error at or near "WHERE"
LINE 4: WHERE AVG(Milliseconds) > 200000
        ^

HAVING

SELECT Composer, AVG(Milliseconds)
FROM Track
GROUP BY Composer
HAVING AVG(Milliseconds) > 200000

| composer    | avg    |
|-------------|--------|
| George Duke | 274155 |
| Miles Davis | 391146 |
| R. Carless  | 251585 |
| ...         | ...    |

Restricting group results with HAVING

Having clause flow

HAVING

SELECT Composer, MAX(Milliseconds)
FROM Track
GROUP BY Composer
HAVING MAX(Milliseconds) > 200000

| composer    | max    |
|-------------|--------|
| George Duke | 274155 |
| Miles Davis | 907520 |
| R. Carless  | 251585 |
| ...         | ...    |

Another example

SELECT Composer, SUM(UnitPrice)
FROM Track
WHERE GenreId = 1
GROUP BY Composer
HAVING COUNT(*) > 4

| composer      | sum  |
|---------------|------|
| AC/DC         | 7.92 |
| Chris Cornell | 9.90 |
| Eddie Vedder  | 8.91 |
| ...           | ...  |

Guidelines

Different group functions can be used in SELECT andHAVING
HAVING always has a grouping function

Order of operations:

Rows are filtered by WHERE and GROUP BY
Group function applied to the groups
The groups are filtered by HAVING then outputted

Let's practice!

Introduzione a Oracle SQL