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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
example of add constraint in sqlexample alternative formulation for maxenrolmentsalter table isenrolledonadd constraint maxenrolmentscheck select
row counterparts of table operatorssql does not have counterparts tuple rename tuple projection tuple extension tuple join and tuple compose to
operators on tables and rowsrow extractiontuple from r sql has row subqueries these are just like scalar subqueries except that they may specify more
table comparison - sqlthe following definitions for relation comparisonslet r1 and r2 be relations having the same heading thenr1 sube r2 is
example of unwrap operator - sqlexample here shows how unwrapping can be done in longhand in sqlexample unwrapping in sqlletting contactinfowrapped
example of wrap operator - sqlthe effect of example can be obtained in sql but note that one needs to write down not only the names of the columns
wrapping and unwrapping in sqloperators wrap and unwrap in connection with attributes whose declared types are tuple types example shows how
unnest operator in sqlthe inverse operator of group is ungroup sql has an operator unnest that can be used for similar purposes but its method of
example of group by and collect operatorexample using group by and collect to obtain cer2select courseidcast collect row studentid markas row
example of groupby operatorexample how many students sat each examusing group by natural left join and coalesceselect courseid coalesce n 0 as nfrom
example of coalesce operatorexample give the total of marks for each exam simplified solutionselect courseidcoalesce select sum markfrom exammark as
example of cast operator so long as cast is used as shown we could obtain the total marks for each exam in similar fashion using sum mark as
example of using aggregation on nested tablesexample how many students sat each examwith cer as select courseid cast table select distinct studentid
using aggregation on nested tablesexample is the most direct translation of its counterpart in the theory book that can be obtained in sql but it is