VARCHAR(n) Length Compatibility Boundary When Migrating to DuckDB

Short answer

DuckDB does not enforce the n in VARCHAR(n), and no session or database setting enables strict length enforcement. VARCHAR(n), VARCHAR, and TEXT are treated as synonymous unbounded string types in current stable releases. To preserve strict-length semantics from PostgreSQL or MySQL, add an explicit CHECK constraint.

Confirmed behavior and assumptions

Confirmed: inserting a string longer than n into a VARCHAR(n) column succeeds. PRIMARY KEY, UNIQUE, and other constraints do not imply a length cap. Assumption: this applies to recent stable DuckDB releases; behavior in very old or preview builds is not verified here.

Migration pattern

1. Declare the column as VARCHAR(n) or TEXT for compatibility.
2. Add CHECK (length(column_name) <= n) to the same CREATE TABLE statement.
3. Update application error handling if it expects database rejection of oversized strings.

CREATE TABLE users (
    username VARCHAR(32) CHECK (length(username) <= 32)
);

Verification

1. CREATE TABLE t (c VARCHAR(10));
2. INSERT INTO t VALUES ('12345678901'); - expect success without a check.
3. Recreate the table with CHECK (length(c) <= 10); the same insert should fail.

This draft requires verification against your DuckDB release before production use. One missing diagnostic detail: which DuckDB version you are targeting, because enforcement behavior could differ in unreleased or pre-release builds.