Migrate Data Between Databases with CSV

Why CSV Works as a Migration Bridge

Native dump formats differ between engines. CSV is universal: every database can export it and every database can import it. For many table-level migrations—especially when types are simple and volume is moderate—CSV is the pragmatic bridge while you rebuild schemas on the target.

It is not ideal for every object (procedures, triggers, complex types), but for row data it is hard to beat.

Migration Phases

Treat migration as a project with checkpoints, not a single COPY command.

• Inventory tables, volumes, PII, and dependencies (FK order).
• Design target schema and column maps.
• Dry-run export → transform → stage → reconcile on a copy.
• Full load + incremental catch-up if downtime must be short.
• Cutover, verify, and keep a rollback path.

Step-by-Step: Export from the Source

Export table-by-table in dependency order (parents before children).

-- PostgreSQL example
COPY (
  SELECT id, email, created_at
  FROM users
) TO '/tmp/users.csv'
WITH (FORMAT csv, HEADER true, ENCODING 'UTF8');

Map and Transform

Schemas rarely match 1:1. Build an explicit mapping sheet: source column → target column → transform rule.

Step-by-Step: Load the Target

Disable or defer secondary indexes and FK checks only if your runbook allows it—and re-enable them before cutover.

• Create staging tables on the target.
• Bulk load CSV (COPY / LOAD DATA / INSERT batches).
• Run transform SQL into final tables.
• Rebuild indexes and validate constraints.
• Reconcile counts and checksums against source.

Reconciliation Checks

Never declare victory on "it loaded."

-- Counts
SELECT 'users' AS t, COUNT(*) FROM users
UNION ALL
SELECT 'orders', COUNT(*) FROM orders;

-- Aggregate checksum example
SELECT COUNT(*), SUM(amount), MIN(created_at), MAX(created_at)
FROM orders;

-- Orphan children
SELECT COUNT(*) FROM orders o
LEFT JOIN users u ON u.id = o.user_id
WHERE u.id IS NULL;

Cutover Strategies

Pick based on downtime tolerance.

Real-World Examples

Migrations where CSV carried the weight.

Common Mistakes

These cause painful rollbacks.

• Migrating child tables before parents.
• Ignoring character set differences (utf8mb4 vs UTF-8).
• Losing boolean/date semantics in Excel mid-flight.
• No reconciliation beyond "file uploaded."
• No rollback: source decommissioned too early.

Best Practices

Migration hygiene.

• Script every export/transform/load step.
• Keep mapping docs next to the scripts in Git.
• Dry-run on a full-size copy first.
• Preserve source until soak time passes.
• Encrypt files in transit and at rest—CSV is often full of PII.

Why Use Convert CSV Online?

Convert CSV Online is free, browser-based, and requires no account for everyday conversions. Use it to inspect extracts, reshape columns between schemas, convert samples to Excel for stakeholder sign-off, or generate SQL for smaller tables. Client-side workflows work on Windows, macOS, and Linux browsers.

Conclusion

CSV migrations succeed with ordered exports, explicit maps, staging loads, and hard reconciliation—not with hope. Automate the path, verify twice, then cut over.