PostgreSQL:Constraints

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• sql - How to add a length constraint to a text field - Stack Overflow

When you create the table you can do something of this sort,

CREATE TABLE names (
  name text CONSTRAINT namechk CHECK (char_length(name) <= 255)
)

(namechk is just a name for the constraint)

Same goes for ALTER TABLE for example:

ALTER TABLE names
  ADD CONSTRAINT namechk CHECK (char_length(name) <= 255);

Check Constraints

• PostgreSQL: Documentation: 15: 5.4. Constraints # 5.4.1. Check Constraints

on delete cascade

• MySQL :: foreign key 사용하기, on update cascade, on delete set null
• on delete cascade
• on delete set null

on update cascade

• MySQL :: foreign key 사용하기, on update cascade, on delete set null
• on update cascade
• on update set null

See also

• PostgreSQL

Favorite site

• PostgreSQL: Documentation: 15: 5.4. Constraints