Valores NULL

SQL intermedio

Jasmin Ludolf

Data Science Content Developer, DataCamp

Valores ausentes

COUNT(field_name) incluye solo los valores no ausentes
COUNT(*) incluye valores ausentes

null

Valores ausentes:
- Error humano
- Información no disponible
- Motivo desconocido

null

SELECT COUNT(*) AS count_records
FROM people;

|count_records|
|-------------|
|8397         |

SELECT *
FROM people;

|id|name              |birthdate |deathdate|
|--|------------------|----------|---------|
|1 |50 Cent           |1975-07-06|null     |
|2 |A. Michael Baldwin|1963-04-04|null     |
|3 |A. Raven Cruz     |null      |null     |
...

IS NULL

SELECT name
FROM people
WHERE birthdate IS NULL;

|name         |
|-------------|
|A. Raven Cruz|
|A.J. DeLucia |
|Aaron Hann   |
...

IS NOT NULL

SELECT COUNT(*) AS no_birthdates
FROM people
WHERE birthdate IS NULL;

|no_birthdates|
|-------------|
|2245         |

SELECT COUNT(name) AS count_birthdates
FROM people
WHERE birthdate IS NOT NULL;

|count_birthdates|
|----------------|
|6152            |

COUNT() comparado con IS NOT NULL

SELECT 
   COUNT(certification) 
   AS count_certification
FROM films;

|count_certification|
|-------------------|
|4666               |

SELECT 
   COUNT(certification) 
   AS count_certification
FROM films
WHERE certification IS NOT NULL;

|count_certification|
|-------------------|
|4666               |

Conceptos principales sobre NULL

Los valores NULL son valores ausentes.
Son muy frecuentes.
Puedes usar IS NULL o IS NOT NULL para:
- Identificar los valores que faltan
- Seleccionar valores ausentes
- Excluir valores ausentes

¡Vamos a practicar!

SQL intermedio