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Adding Table Constraints
ALTER TABLE ENROLMENT ADD CONSTRAINT NameNotNull
CHECK (Name IS NOT NULL) ;
ALTER TABLE ENROLMENT ADD CONSTRAINT PK_StudentId_CourseId
PRIMARY KEY (StudentId, CourseId) ;
Effects of NULL for Table Expression Here's an important distinction between expressions denoting tables and expressions denoting multisets of rows: a table expression cannot
Identifiers You use identifiers to name the PL/SQL program items and units that include constants, variables, cursors, exceptions, cursor variables, subprograms, and packages.
%ROWCOUNT When its cursor or cursor variable is opened, the %ROWCOUNT is zeroed. Before the first fetch, the %ROWCOUNT yields 0. Afterward, it yields the number of rows fetche
Natural Join - SQL In the absence of NATURAL JOIN Example has to be replaced by something rather more longwinded, as shown in Example. Example: Joining IS_CALLED and IS_EN
Name Resolution During the compilation, the PL/SQL compiler relates identifiers like the name of a variable with an address or memory location, actual value, or datatype. Th
Effects of NULL for UNIQUE Specification When a UNIQUE specification u for base table t includes a column c that is not subject to a NOT NULL constraint, the appearance of sev
Explicit Cursors The set of rows returned by the query can include zero, one, or multiple rows, depending on how many rows meet your search criteria. Whenever a query returns
Truth Tables: However in propositional logic - here we are restricted to expressing sentences and where the propositions are true or false - so we can check where a particular
PRIMARY KEY: PRIMARY KEY indicates that the table is subject to a key constraint, in this case declaring that no two rows in the table assigned to ENROLMENT can ever have the
Predicate - SQL Consider the declarative sentence-a proposition-that is used to introduce this topic: "Student S1, named Anne, is enrolled on course C1." Recall that th
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