Patrick Ozoh (PhD)

A transaction is a sequence of DML commands that forms a logical unit of work Example: transferring money from one bank account to another Transaction Management A transaction is a sequence of DML commands that forms a logical unit of work Example: transferring money from one bank account to another Some Definitions Atomicity - a transaction must execute completely or not at all Consistency - once a transaction completes successfully, the database must be in a consistent state Isolation: A transaction must not be affected by other transactions that are executing concurrently Durability: Once a transaction compketes successfully, its effect must persist even in the presence of system failures Concurrency control Concurrency control is a database management systems (DBMS) concept meant to coordinate simultaneous transactions while preserving data integrity. Control protocols ensures atomicity, isolation, and serializability of concurrent transactions Concurrency control protoc

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  SQL (Structured Query Language) is THE standard DML for relational database products. The query language is based on relational algebra, but borrows from tuple relational calculus. Topics: •  the data-definition language (DDL) - creating, deleting and modifying relation   schemas •  the data-manipulation language (DML) - the query   language •  modification of relations (insert, delete,   update) •  integrity constraints (domain constraints and foreign   keys) •  creation and use of   views •  transaction   control •  application   programming Five major standards have been defined for SQL: •  SQL-86 •  SQL-89 •  SQL-92 •  SQL:1999 •  SQL:2003 Each standard is essentially a superset of the previous ones. Most major commercial systems support essentially the SQL-92 standard along with some part of the SQL:1999 and SQL:2003 standards. In the following examples, we continue to use the flyshop database with the following schema (primary  key attributes   underlined):   schema name attrib