What is a transaction in a database?

A database transaction is a logically connected sequence of operations (such as insert, update, delete) that is executed as a single unit. A transaction has four main properties (ACID):

• Atomicity: all operations within the transaction are either fully completed or not executed at all.
• Consistency: the transaction transforms the database from one correct state to another.
• Isolation: concurrent transactions do not affect each other, and their results are not mixed.
• Durability: after a transaction successfully completes, the changes are saved in the database and are not lost.

Example in Go using a database and transactions:

import (
    "database/sql"
    _ "github.com/lib/pq" // PostgreSQL driver
    "log"
)

func transferFunds(db *sql.DB, fromAccount, toAccount string, amount float64) error {
    tx, err := db.Begin()
    if err != nil {
        return err
    }

    defer func() {
        if p := recover(); p != nil {
            tx.Rollback()
            panic(p)
        } else if err != nil {
            tx.Rollback()
        } else {
            err = tx.Commit()
        }
    }()

    _, err = tx.Exec("UPDATE accounts SET balance = balance - $1 WHERE id = $2", amount, fromAccount)
    if err != nil {
        return err
    }

    _, err = tx.Exec("UPDATE accounts SET balance = balance + $1 WHERE id = $2", amount, toAccount)
    if err != nil {
        return err
    }

    return err
}

Here, the withdrawal and deposit operations are performed within a single transaction to prevent partial data updates.