Constraints

This document provides information about the constraints supported in Oxibase, based on evidence from test files and implementations.

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Table of Contents

1. PRIMARY KEY
2. NOT NULL
3. UNIQUE
4. FOREIGN KEY
   1. Referential Actions
5. DEFAULT
6. CHECK

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Oxibase supports several column and table constraints:

PRIMARY KEY

Uniquely identifies each row in a table:

CREATE TABLE users (
    id INTEGER PRIMARY KEY,
    name TEXT
);

-- With AUTO_INCREMENT
CREATE TABLE orders (
    id INTEGER PRIMARY KEY AUTO_INCREMENT,
    product TEXT
);

NOT NULL

Ensures a column cannot contain NULL values:

CREATE TABLE users (
    id INTEGER PRIMARY KEY,
    name TEXT NOT NULL,
    email TEXT NOT NULL
);

UNIQUE

Ensures all values in a column are distinct:

CREATE TABLE users (
    id INTEGER PRIMARY KEY,
    email TEXT UNIQUE,
    username TEXT UNIQUE
);

-- Duplicate values will be rejected
INSERT INTO users VALUES (1, 'alice@test.com', 'alice');
INSERT INTO users VALUES (2, 'alice@test.com', 'bob');  -- Error: unique constraint failed

FOREIGN KEY

Enforces referential integrity between columns in two tables. A foreign key ensures that a value in the referencing column must either be NULL or exist in the referenced column (which is typically a PRIMARY KEY or UNIQUE constraint).

CREATE TABLE users (
    id INTEGER PRIMARY KEY,
    name TEXT
);

CREATE TABLE orders (
    id INTEGER PRIMARY KEY,
    user_id INTEGER,
    -- Defines a foreign key inline
    FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE
);

-- Adding a constraint after table creation
ALTER TABLE orders ADD CONSTRAINT fk_user FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE SET NULL;

Referential Actions

You can define behaviors when the referenced row is deleted (ON DELETE) or updated (ON UPDATE):

• RESTRICT: (Default) Prevents the deletion or update of a referenced row if dependent rows exist. Returns a referential integrity violation error.
• CASCADE: Deletes or updates the dependent rows automatically when the referenced row is deleted or updated.
• SET NULL: Sets the foreign key column in dependent rows to NULL when the referenced row is deleted or updated (requires the column to be nullable).
• NO ACTION: Similar to RESTRICT, prevents the operation.

-- Prevents deleting a department if it has employees
CREATE TABLE employees (
    id INTEGER PRIMARY KEY,
    dept_id INTEGER,
    FOREIGN KEY (dept_id) REFERENCES departments(id) ON DELETE RESTRICT
);

DEFAULT

Specifies a default value when none is provided:

CREATE TABLE users (
    id INTEGER PRIMARY KEY,
    name TEXT DEFAULT 'Unknown',
    active BOOLEAN DEFAULT true,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

-- Insert without specifying defaulted columns
INSERT INTO users (id) VALUES (1);
-- Result: id=1, name='Unknown', active=true, created_at=<current time>

Supported default values:

• Literal values: 'text', 123, 3.14, true, false
• NULL
• CURRENT_TIMESTAMP or NOW() for timestamps

CHECK

Validates that values satisfy a condition (column-level constraint):

CREATE TABLE employees (
    id INTEGER PRIMARY KEY,
    age INTEGER CHECK(age >= 18 AND age <= 120),
    salary FLOAT CHECK(salary > 0),
    status TEXT CHECK(status IN ('active', 'inactive', 'pending'))
);

-- Valid insert
INSERT INTO employees VALUES (1, 25, 50000, 'active');

-- Invalid insert - fails CHECK constraint
INSERT INTO employees VALUES (2, -5, 50000, 'active');
-- Error: CHECK constraint failed for column age: (age >= 18 AND age <= 120)

Note: CHECK must be specified as a column constraint (inline with column definition), not as a table-level constraint.