How to combine 'union' and 'orderBy'

const a = db.select({ transaction: onlineSales.transactionId }).from(onlineSales);
const b = db.select({ transaction: inStoreSales.transactionId }).from(inStoreSales);
const result = await unionAll(a, b).orderBy( across resulting rows ??? );

const a = db.select({ transaction: onlineSales.transactionId }).from(onlineSales);
const b = db.select({ transaction: inStoreSales.transactionId }).from(inStoreSales);
const result = await unionAll(a, b).orderBy( across resulting rows ??? );