Difference between revisions of "SQL"
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| − | '''SQL''', which stands for "Structured Query Language," is a [[computer language]] for [[relational database]] systems. It was first developed at [[IBM]]. | + | '''SQL''', which stands for "Structured Query Language," is a [[computer language]] for [[relational database]] systems. It was first developed by EF Codd at [[IBM]]. |
In 1986 the American National Standards Institute ([[ANSI]]) promulgated standards for SQL, and since then revisions have been approved by the International Organization for Standardization ([[ISO]]). | In 1986 the American National Standards Institute ([[ANSI]]) promulgated standards for SQL, and since then revisions have been approved by the International Organization for Standardization ([[ISO]]). | ||
SQL was immensely successful, and is supported by a number of database systems, including [[MySQL]]. MySQL is one of the two databases supported by [[MediaWiki]] (the other being PostgreSQL),<ref>http://www.mediawiki.org/wiki/Manual:LocalSettings.php#Database_settings</ref> the software behind a number of wiki-based systems. | SQL was immensely successful, and is supported by a number of database systems, including [[MySQL]]. MySQL is one of the two databases supported by [[MediaWiki]] (the other being PostgreSQL),<ref>http://www.mediawiki.org/wiki/Manual:LocalSettings.php#Database_settings</ref> the software behind a number of wiki-based systems. | ||
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| + | == Transactions == | ||
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| + | A transaction may include several SQL statements, but the statements are processed in an all-or-nothing fashion. The transaction represents logical work like a customer purchasing a product. For example, the statements may include adding the purchase price to the customer's account, and subtracting the product from inventory. If either statement is executed, they must both be executed, and if either statement is aborted, they must both be aborted. This is achieved by using the COMMIT statement and the ROLLBACK statement. Once all of the statements to execute for the current transaction have been entered, the COMMIT statement is entered, and the transaction is committed to the database. If any of the statements in the transaction cannot be completed, the entire transaction is rolled back, and none of the statements take effect. | ||
==References== | ==References== | ||
Revision as of 17:15, October 25, 2007
SQL, which stands for "Structured Query Language," is a computer language for relational database systems. It was first developed by EF Codd at IBM.
In 1986 the American National Standards Institute (ANSI) promulgated standards for SQL, and since then revisions have been approved by the International Organization for Standardization (ISO).
SQL was immensely successful, and is supported by a number of database systems, including MySQL. MySQL is one of the two databases supported by MediaWiki (the other being PostgreSQL),[1] the software behind a number of wiki-based systems.
Transactions
A transaction may include several SQL statements, but the statements are processed in an all-or-nothing fashion. The transaction represents logical work like a customer purchasing a product. For example, the statements may include adding the purchase price to the customer's account, and subtracting the product from inventory. If either statement is executed, they must both be executed, and if either statement is aborted, they must both be aborted. This is achieved by using the COMMIT statement and the ROLLBACK statement. Once all of the statements to execute for the current transaction have been entered, the COMMIT statement is entered, and the transaction is committed to the database. If any of the statements in the transaction cannot be completed, the entire transaction is rolled back, and none of the statements take effect.