Database Engine: The part of the DBMS that works with the data
An engine typically has code that can search, read, write, index and otherwise execute the actual
interaction with the information. A database engine performs the largest share of work in most
databases and thus it is the subject of an intense optimization effort by the DBMS creators. Some of the
most advanced DBMS have engines which can self-optimize after monitoring the actual conditions after
deployment. A DBMS will have additional features that are not part of the data engine, including query
analyzing, replication and back-up tools, user management, security tools and performance monitoring.
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Results: The term "Result" frequently confuses folks learning SQL because the term can be
used in three ways:
First, and most common, we mean a set of data that is returned after a front end sends a
SQL statement to a DBMS. You ask for "The first and last names of all the employees that
started after 1995" and you get back a block of characters (a recordset) containing those
But what if the SQL statement instructs the DBMS to modify data rather than just read it?
The second case is when the "result" refers to a change in the data. We do not necessarily
receive any characters back from the DBMS although we may get a status message noting
that the operation was successful.
Third, we may make changes to the data and have the DBMS report back to us on the
changes. Frequently this is a notice of how many records were changed or what errors
arose or a True/False that the SQL statement was executed successfully. In this case
we get a result back, but it is not actual data; it is a message or code indicating the
number of records changed, an error or success.
In this book we use the term all three ways since there is no common alternative vocabulary.
"SQL" and "SQL Server": SQL is the name of an open-standard language for communicating
with databases. Microsoft SQL Server and Sybase SQL Server are proprietary DBMS products
that can handle SQL statements. Microsoft SQL Server is popular, but it is only one of many
DBMS that can handle your data and your SQL statements.