Informix Error -286

Reasons / Common Causes

-286 is a clear, well-defined restriction: a column that's part of a primary key can never have NULL as its default value — this follows directly from what a primary key means (every row must have a real, non-null value for it).

1. Explicitly setting a NULL default value on a primary key column — the direct cause.
2. A generic table-definition template or schema-generation script that sets a NULL default uniformly across all columns, without excluding primary key columns specifically.
3. A schema ported from another system with different primary-key/default-value rules.
4. Confusion between "no default specified" (fine) and "default explicitly set to NULL" (not allowed for primary key columns) — these are different things, and only the latter triggers this error.

Solutions / Resolution

1. Don't set a NULL default value for a primary key column — either omit the DEFAULT clause entirely, or specify a genuine non-null default if one is actually needed.
2. Review schema-generation templates or scripts to exclude primary key columns from any uniform "default to NULL" logic.
3. For SERIAL/SERIAL8/BIGSERIAL primary keys, the auto-generated value already serves as the effective default — don't attempt to also specify an explicit NULL default on top of that.

Examples

The disallowed default

CREATE TABLE orders
(
    order_id INTEGER DEFAULT NULL,
    PRIMARY KEY (order_id)
);
-- -286: order_id is part of the primary key and can't default to NULL

Fix — omit the default entirely, or use a genuine non-null value:

CREATE TABLE orders
(
    order_id INTEGER,
    PRIMARY KEY (order_id)
);

A generic template mistakenly applying NULL defaults everywhere

-- A schema-generation tool defaults every column to NULL uniformly,
-- including the primary key column
CREATE TABLE customer (id INTEGER DEFAULT NULL, name VARCHAR(50) DEFAULT NULL, PRIMARY KEY (id));
-- -286

Excluding primary key columns from the tool's default-value logic resolves this.

Diagnostic Checks

1. Review the column or table definition for a DEFAULT NULL clause specifically on a primary key column.

Related Errors / Related Topics

• -269 — "Cannot add column column-name that does not accept nulls." Another column-default/constraint restriction in the same general category.
• -100 — "ISAM error: duplicate value for a record with unique key." Related through the same general primary-key/uniqueness family.

Simply remove the NULL default from the primary key column — there's no legitimate use case for it, since a primary key can never actually hold a null value.