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Multiple Assignment- SQL
SQL supports multiple assignment to local variables and also applies multiple assignment semantics in SET clauses of UPDATE statements, but does not support multiple assignment in connection with updates on table targets. Thus, SQL has no counterpart to the theory book's Example, simultaneously deleting from both COURSE and IS_ENROLLED_ON. If we assume that there must be at least one enrolment for each course, and that students can enroll only on existing courses, deferred constraint checking has to be used, as shown in Example here.
Example: Withdrawing course C3 and deleting any enrolments on C3
Assume the definition of IS_ENROLLED_ON includes
CONSTRAINT Course_must_exist_for_enrolment
FOREIGN KEY (CourseId) REFERENCES COURSE ON DELETE NO ACTION
and the definition of COURSE includes
CONSTRAINT Enrolment_must_exist_for_course
CHECK ( CourseId IN (SELECT CourseId FROM IS_ENROLLED_ON)
Scoping Within the similar scope, all the declared identifiers should be unique. So, even if their datatypes differ, the variables and parameters cannot share the similar name.
UTL_FILE: The Package UTL_FILE permits your PL/SQL programs to read & write operating system (OS) text files. It gives a restricted version of the standard OS stream file I/O,
Example of Tables within a Table - SQL Example: Obtaining C_ER from COURSE and EXAM_MARK SELECT CourseId, CAST (TABLE (SELECT DISTINCT StudentId, Mark FROM EXAM_MARK AS EM
BETWEEN and NOT BETWEEN Operator in SQL Example: Restricting exam marks to between 0 and 100 CREATE ASSERTION Marks_between_0_and_100 CHECK (NOT EXISTS (SELECT * FROM
Updating a Variable Assignment of an attribute value in a variable of a structured type Synatx: SET SN.C = 'S2'; As in Example the entire statement is equivalent to a
Indeterminacy in SQL Some SQL expressions are actually not function invocations at all in the mathematical sense, being indeterminate-invocations operating on identical input
Why Use Cursor Variables ? Primarily, you use the cursor variables to pass the query result sets between the PL/SQL stored subprograms and different clients. Neither PL/SQL nor
Using Savepoints The scope of the savepoint is a transaction in which it is defined. The Savepoints defined in the major transaction are not related to the savepoints defined
Advantages of Exceptions Using the exceptions for the error handling has many benefits. Without an exception handling, every time you issue a command, you should ensure for th
Naming Conventions The similar naming conventions apply to all PL/SQL program items and units including the variables, cursors, constants, cursor variables, procedures, exception
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