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docs: add FOR UPDATE clause to MySQL transaction example #4035

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7 changes: 6 additions & 1 deletion docs/howto/transactions.md
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@@ -1,6 +1,10 @@
# Using transactions
In the code generated by sqlc, the `WithTx` method allows a `Queries` instance to be associated with a transaction.

## Locking Reads in Transactions

When you query data and then update related data within the same transaction, regular `SELECT` statements may not provide adequate protection against race conditions. For MySQL/InnoDB, using `SELECT ... FOR UPDATE` provides exclusive locks on the selected rows, preventing other transactions from modifying them until your transaction completes.

For example, with the following SQL structure:

`schema.sql`:
Expand All @@ -15,7 +19,8 @@ CREATE TABLE records (
```sql
-- name: GetRecord :one
SELECT * FROM records
WHERE id = $1;
WHERE id = $1
FOR UPDATE;

-- name: UpdateRecord :exec
UPDATE records SET counter = $2
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