Informix Error -703: Primary key on table table-name has a field with a null key value.

Reasons / Common Causes

-703 fires in two related situations, per the official guidance: an INSERT/UPDATE attempting to put a NULL value into a column that's part of a primary key, or an ALTER TABLE ... ADD CONSTRAINT PRIMARY KEY against a table that already has a NULL in one of the intended key columns.

1. An INSERT/UPDATE supplying NULL for a primary-key column — per the official guidance, primary keys never allow NULL in any of their columns, by definition.
2. ALTER TABLE ... ADD CONSTRAINT PRIMARY KEY against existing data that already contains a NULL in one of the columns being made the key — per the official guidance, the constraint can't be added while that data exists.

Solutions / Resolution

1. Supply a non-NULL value for every primary-key column on insert/update.
2. For an existing table gaining a primary key, find and fix rows with NULL in the intended key column(s) first:

   SELECT * FROM orders WHERE order_id IS NULL;
   

   update or delete those rows before retrying ALTER TABLE ... ADD CONSTRAINT PRIMARY KEY.

Examples

Inserting NULL into a primary-key column

INSERT INTO orders (order_id, status) VALUES (NULL, 'pending');
-- -703: order_id is the primary key and can't be NULL

Adding a primary key against data with an existing NULL

ALTER TABLE orders ADD CONSTRAINT PRIMARY KEY (order_id);
-- -703: some existing rows already have order_id IS NULL

SELECT * FROM orders WHERE order_id IS NULL;
-- fix or remove those rows, then retry the ALTER TABLE

Diagnostic Checks

1. Query the table for existing NULLs in the intended primary-key column(s) before adding the constraint, or check the specific value being inserted/updated if the error is on a live INSERT/UPDATE.

Related Errors / Related Topics

• -704 — "Primary key already exists on the table." A related primary-key error, about a table already having one rather than a NULL value in the key.

A NULL is never allowed in any primary-key column — clean up existing NULLs before adding the constraint, or supply a real value on insert/update.