Transaction Anamolies

• Dirty reads occur when:
  1. Transaction A inserts a row into a table.
  2. Transaction B reads the new row.
  3. Transaction A rolls back.
  Transaction B may have done work to the system based on the row inserted by transaction A, but that row never became a permanent part of the database.
• Nonrepeatable reads occur when:
  1. Transaction A reads a row.
  2. Transaction B changes the row.
  3. Transaction A reads the same row a second time and gets the new results.
• Phantom reads occur when:
  1. Transaction A reads all rows that satisfy a WHERE clause on an SQL query.
  2. Transaction B inserts an additional row that satisfies the WHERE clause.
  3. Transaction A re-evaluates the WHERE condition and picks up the additional row.