ORA-00001: unique constraint (SCHEMA.PK_X) violated
An insert/update duplicated a value in a unique or primary key constraint.
Exact message you may see
unique constraint violated
Seen on:
SQL
Meaning
Common when sequences fall behind manually inserted ids or seeds run twice.
Common causes
- Duplicate value
- Sequence behind existing max(id)
- Re-run seeds
⚡ Quick fix
- Use MERGE for upserts
- Advance the sequence past max(id)
- Handle as "already exists"
Detailed fix by platform
SQL
ALTER SEQUENCE orders_seq RESTART START WITH 100001; -- Oracle 18c+
How to diagnose
- Constraint — Which one?
- Sequence — Behind the data?
🔧 Still not fixed?
Many errors look alike. If the steps above didn’t solve it, one of these is probably what you’re facing:
Similar errors
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Other ways to find it
Where this error sits
Origin: Data. Errors that are often confused with or caused by this one (click to open):
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Last updated 12 Oct 2026