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example of table literal - sqlexample a table literal correct versionvaluess1 c1 annes1 c2 annes2 c1 boriss3 c3 cindys4 c1 devindernow the question
table literals - sqlone might expect sql to support table literals in the manner illustrated in example 22 but in fact that is not a legal sql
multiset types - sqlan sql multiset is what in mathematics is also known as a bag-something like a set except that the same element can appear more
usefulness of data type in sql as in most computer languages a type can be used for constraining the values that are permitted to be used for some
data types in sql - xml array row binary large object for arbitrarily large bit strings xml for xml documents and fragments array types for arrays
data types in sql - interval booleaninterval for values denoting not intervals but durations in time such as 5 years 3 days 2 minutes and so
data types in sql - timestamptimestamp for values representing points in time on a specified uniform scale date is used for timestamps on a scale of
data types in sql - integerinteger or synonymously int for integers within a certain range sql additionally has types smallint and bigint for
data types in sql - decimaldecimal numeric real float and various other terms for various sets of rational numbers when these key words are specified
data types in sql - charactercharacter or synonymously char for character strings when this type is to be the declared type of something eg a column
data types in sqlsqls concept does not differ significantly from that defined in the theory book apart from that business concerning null however the
cause of indeterminacy in sqlone root cause of indeterminacy in sql lies in its implementation of comparison for equality for certain system-defined
indeterminacy in sqlsome sql expressions are actually not function invocations at all in the mathematical sense being indeterminate-invocations
example of null operator - nino ruleif we wanted to make higherof adhere to null in null out-lets call it the nino rule-we would have to write
effects of null operatoras a general rule-but not a universal one-if null is an argument to an invocation of a system-defined read-only operator then
read-only operator - sqlthe term read-only operator to the mathematical term function here i just need to add that the sql standard reserves the
important distinctionsthe list of important distinctions are given below value versus variable syntax versus semantics variable versus variable
effects of nullthe numeric variable x perhaps of type integer might be assigned null in that case the result of evaluating x 1 is null and so set y
updating by insertionsyntaxinsert into enrolmentvalues sid s4devindercid
updating by replacementsyntaxupdate enrolment set name annwhere studentid sid s1note the use of set as already noted in connection with direct
updating variablesfor assignment sql uses the key word set as in set x x 1 read as set x equal to x1 rather than x x 1 as found in many computer
authorisations - privilegesas relational theory is silent on the issue of authorisation it offers nothing with which sqls vast edifice in support of
equivalences amp rewrite rulesif notice that as well as allowing us to prove trivial theorems and tautologies enable us to establish that certain
tautology - equivalences rulesif there tautologies are not all the time as much easy to note as the one above so than we can use these truth tables
primary keyprimary key indicates that the table is subject to a key constraint in this case declaring that no two rows in the table assigned to