Unique and check constraints
On This Lesson 4 topics
This lesson is planned. The outline below lists the topics it will cover. The full lesson has not been published yet.
In this lesson
write the main constraint types.
Planned topics
not null: the value must exist.unique: no two rows share the value (or combination).foreign key: the referenced row must exist; choose the delete behavior on purpose.check: a rule on the row (price >= 0).- Name constraints (
ux_product_sku) so error messages and handlers are clear.
Draft outline details
Demonstration
alter table product
add constraint ux_product_sku unique (sku),
add constraint ck_product_price check (price >= 0);
alter table order_line
add constraint fk_line_order foreign key (order_id) references orders(id);Check your understanding
Which constraint stops a negative price?
Show answer
A check constraint.
Practice
Apply this lesson with the module's lab, exercises and quiz.
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