Comment gérer des données nulles dans une base de données SQL
Lorsque nous créons une table de cette manière:
CREATE TABLE people (
age INT,
name CHAR(20)
);SQL accepte librement les valeurs vides comme enregistrements:
INSERT INTO people VALUES (null, null);Cela peut être un problème, car nous avons maintenant une ligne avec des valeurs nulles:
age | name
-----+--------
37 | Flavio
8 | Roger
| To solve this, we can declare constrains on our table rows. NOT NULL prevents null values:
CREATE TABLE people (
age INT NOT NULL,
name CHAR(20) NOT NULL
);
If we try to execute this query again:
INSERT INTO people VALUES (null, null);
We’d get an error, like this:
ERROR: null value in column "age" violates not-null constraint
DETAIL: Failing row contains (null, null).
Note that an empty string is a valid non-null value.
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