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update command- sqlloosely speaking update changes some of the column values of some existing rows of its target table thus although some rows
example of except operator - sqlexample like its counterpart in the theory book illustrates the convenience of allowing any table expression to be
insert command in sqlloosely speaking insert takes the rows of a given source table and adds them to the specified target table retaining all the
updating tables in sqlthe topic of updating by describing the assignment operator in tutorial d sql uses a different syntax for assignment using the
example of foreign key constraintexample alternative formulation for 63 as a foreign key constraintalter table exammarkadd constraint
example of when or then constraintsa concrete example showing how sql supports whenthen constraintscreate table salhistory empno char 6salary integer
when or then key constraintssuppose a table has two columns representing a period of time throughout which the information conveyed by the other
effects of null for unique specificationwhen a unique specification u for base table t includes a column c that is not subject to a not null
keys in sqlsql support for keys in the following respectssql does not require at least one key for every base table if no key is explicitly declared
primary key - sqla primary key specification carries an implicit not null constraint on each column of the specified key when more than one key
example of shorthand for a row constraintexample shorthand for a row constraintalter table exammarkadd constraint markinrangecheck mark between 0 and
check constraints in sqla check constraint is a table constraint defined using the key word check as already illustrated in several examples in this
effects of null in aggregate operator - sqllet aggopx be an invocation of some aggregate operator aggop in sql where x is an expression usually an
effects of null for table expressionheres an important distinction between expressions denoting tables and expressions denoting multisets of rows a
between and not between operator in sqlexample restricting exam marks to between 0 and 100create assertion marksbetween0and100check not exists select
use of table comparisons - sqltable comparisons where it is noted that although table expressions cannot be compared we have table t to convert a
example of not exists operator - sqlexample is a translation into sql of the corresponding example which is included there merely to show that for
example of alternative formulation as a table constraintexample alternative formulation as a table constraintalter table exammarkadd constraint
example of not exists in sqlexample use of not existscreate assertion mustbeenrolledtotakeexamalternative1check not exists select studentid
use of count in sqlit describes and discusses various general methods of expressing constraints eventually noting that support for with relation
procedural constraint enforcement triggers sql has an alternative method of addressing database integrity involving event-driven procedural code the
use of table expressions - expressing constraint conditionswith the exception of key constraints the examples in the theory book all explicitly
when are constraints checked under the model constraints are conceptually checked at all statement boundaries and only at statement boundaries by
not enforced table constraintsa constraint that is not enforced is not really a constraint within the meaning of the act but sql does have such a
example of check constraintsexample workaround for when subqueries not permitted in check constraintscreate function nomorethan20000enrolments