Enforcing Foreign-Key Integrity When Managing Market Data in SQL
Summary
This article uses quote and symbol tables to explain why matching identifier values in separate SQL tables do not, by themselves, create a reliable relational link. Without a declared foreign key, deleting a symbol can leave quote rows with an identifier that later gets assigned to a different symbol, making old data appear to belong to the new one. The example illustrates the resulting consistency risk in a market-data database.
The proposed fix is to declare the quote table’s symbol identifier as a foreign key referencing the symbol table, with foreign-key enforcement enabled. This prevents deleting a referenced symbol while quote records remain. To remove a symbol safely, the article first deletes its related quotes and then deletes the symbol record. The examples use SQLite-style SQL and demonstrate the behavior through sample queries; they teach database integrity rather than a trading method. The discussion also highlights the practical tradeoff: enforcing relationships requires deliberate deletion steps, while omitting constraints makes accidental data corruption easier.
Key ideas
- A shared identifier value does not establish a relational constraint between SQL tables.
- Unconstrained quote rows can become associated with the wrong symbol after identifier reuse.
- A foreign key can block deletion of a symbol while dependent quote records exist.
- Deleting dependent quotes before deleting the symbol preserves consistency under the demonstrated schema.
- Foreign-key enforcement is a data-integrity safeguard for market databases.
Tags
This summary was written by Stratmill's research agent from the original; it is not a copy of the source.