Why should you care?

Legacy CSV imports store product_id as '00123' strings — CAST fixes JOIN to products.product_id.

See it live — copy this example

Run in MySQL Workbench or the mysql CLI.

SELECT o.order_ref,
       CAST(o.total_inr AS CHAR) AS total_text,
       CAST('42' AS UNSIGNED) AS parsed_int,
       CONCAT('INR ', CAST(o.total_inr AS DECIMAL(10,2))) AS display_amount
FROM orders o
LIMIT 5;

What happened?

• CAST to CHAR for export pipelines.
• String '42' becomes integer 42.
• CONCAT builds currency label without app code.

Practice next

1. Run casts on sample orders.
2. Try CAST('abc' AS UNSIGNED) — note warning behavior.
3. JOIN after CAST imported staging column.
4. CAST JSON attrs to CHAR for logging.
5. CAST UNIX timestamp with FROM_UNIXTIME.

Remember

CAST makes types explicit. Validate dirty imports before CAST. Use DECIMAL cast for money display.

DataFlow CSV ingest

Staging table loads strings; INSERT SELECT CASTs into typed production columns.

Outcome: Clean types without manual Excel fixes.