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interesting properties of cross join - sqlcompare these with the interesting properties of join cross join is associative but not commutative unlike
definition of cross join - sqllet s t1 cross join t2 where t1 and t2 are table expressions optionally accompanied by range variables thennote here t
join and and in sqlin this section is all about one operator join sqls closest counterpart natural join has already been covered here we look at
relational operators and logical operatorsit prepares the ground for subsequent sections in which each specific relational operator is paired with
relational algebra - sqlit describes some operators that together constitute an algebra that is not only relationally complete but also irreducibly
existential quantification - sqlexistential quantification-stating that something is true of at least one object under consideration-can be expressed
quantification in sqlto quantify something as the theory book has it is to state its quantity to say how many of it there are for example in tutorial
logical connectives - sqlsqls extended truth tables in which the symbol for unknown appears along with the usual t and f negation not not conjunction
deriving predicates from predicates in sqlthe corresponding section in the theory book describes how predicates can be derived from predicates using
table represents an extension - sqlit describes how each tuple in a relation represents a true instantiation of some predicate and each true
substitution and instantiation - sqlit shows how null might appear in substitution for a parameter of a predicate and how it might thus participate
predicate - sqlconsider the declarative sentence-a proposition-that is used to introduce this topic student s1 named anne is enrolled on course
updating a variableassignment of an attribute value in a variable of a structured typesynatxset snc s2as in example the entire statement is
assignment source not a literal - variablesyntaxset sn sid substring snc from 1 for
assignment of variable - updating a variablesyntaxset sn sid s2this can obviously be read as set the variable sn to be equal in value to sid s2
adding table constraints alter table enrolment add constraint namenotnullcheck name is not null alter table enrolment add constraint
effect of anonymous columnsnow recall that a values expression denotes a table with undefined column names if an initial value is to be specified
creating a tablesyantaxcreate table enrolmentstudentid sidname varchar 30 not nullcourseid cidprimary key studentid courseid explanation
variable declaration - sqlsqls support for variables is very similar to tutorial ds except that the syntax for creating persistent variables-base
type versus representation confusion in sqlthis describes how a value might have two or more distinct representations for example user-defined type
third step at defining type sid in sqlcreate domain sid as varchar5check value is not null andsubstringvalue from 1 for 1 s andcastsubstringvalue
second step at defining type sid in sql create type sid as varchar5 explanation type sid announces that a type named sid is being defined to the
first step at defining type sid in sqlcreate type sid as c varchar5 explanation type sid announces that a type named sid is being defined to the
data types and representationsthis explains the concept possible representation abbreviated possrep and explains how these can be used in conjunction
effects of null in table literalwhen a values expression appears as the source value for an sql insert statement the key word null can appear as a