Day 12. DDL code style and best practices

1. Make table creations queries in separate files. One file = one query.

2. Move constrains creation from table creation query. Each table must be created before applying constraints.

3. If it is possible, consider compatible with previous versions and migration.

4. Adhere to naming conventions and watch code style.

5. Watch reproducibility of results, any query should work same kind when running twice or more times. E.g., when we run a table creation query a second time in a row, we should create it each time same without errors or raising exceptions.

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