Database Reference
In-Depth Information
• Update operation: This operation is used to modify tuples in
the relation. The SQL command for the update operation is
described as follows:
UPDATE R
SET [A
1
=a
1
,A
2
=a
2
,...,A
n
=a
n
]
WHERE P
where R is a relation,
A
1
,A
2
,...,A
n
are attributes from relation
R,
a
1
,a
2
,...,a
n
are values from domains of
A
1
,A
2
,...,A
n
that will be updated, and P is the condition of the update
statement that defines tuples that are to be updated.
• Delete operation: This operation is used to delete tuples from
the relation. The SQL command for the delete operation is
described as follows:
DELETE
FROM R
WHERE P
where R is a relation and P is the condition of the delete state-
ment that defines tuples that are to be deleted.
The internal mechanisms of SQL statement processing in the rela-
tional database management system (RDBMS) are presented in the
following five steps:
• The RDBMS parses the SQL statement by dividing it into
individual words and validating the statement syntax.
• The statement is then checked by the RDBMS against the
information schema. In addition, it ensures the user privileges
to execute the statement.
• The next step is the optimization of the SQL statement. The
query optimization process is defined as finding the efficient
way to execute the SQL statement.
• The next step is the generation of the execution plan for the
SQL statement based on the optimization process performed
during the previous step.
• The set of binary instructions created in the previous step is
executed by the RDBMS.
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