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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 WHERE EM.CourseId = C.CourseId)
AS ROW (StudentId SID, Mark INTEGER) MULTISET)
AS ExamResult FROM COURSE AS C
The values for columns such as ExamResult in this example have sometimes been referred to informally as nested tables, being "tables within a table", so to speak. Unfortunately, however, they are not actually tables, but rather multisets of rows. Because of that fact, a column such as ExamResult cannot appear as an element in a FROM clause.
Opening a Cursor Variable The OPEN-FOR statement relates a cursor variable with the multi-row query, executes the query, and then identifies the result set. The syntax for ope
Deleting Objects You can use the DELETE statement to eradicate objects from an object table. To eradicate objects selectively, you use the WHERE clause, as shown below: BEG
Keyword & Parameter Description: PRAGMA: These keywords signify that the statement is a pragma (i.e. compiler directive). The Pragmas are processed at the compile time, n
DELETE Command - SQL Loosely speaking, DELETE removes some existing rows from its target table. Suppose the university decides that course C3 is to be withdrawn. Example shows
Substitution and Instantiation - SQL It shows how NULL might appear in substitution for a parameter of a predicate and how it might thus participate in instantiation of that p
Dynamic SQL: The Most PL/SQL programs do a predictable, specific job. For illustration, a stored procedure may accept an employee number and salary increase, and then update t
Advantages of Subprograms The Subprograms give extensibility; that is, tailor the PL/SQL language to suit your requirements. For illustration, if you require a procedure which
Controlling Autonomous Transactions The first SQL statement in an autonomous routine starts a transaction. Whenever one transaction ends, the next SQL statement starts the oth
COMMIT Statement The COMMIT statement explicitly makes everlasting changes to the database during the present transaction. The Changes made to the database are not considered e
Logical Operators The logical operators AND, NOT, and OR follow the tri-state logic shown in table below. The AND and OR are binary operators; NOT is a unary operator.
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