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Use of COUNT in SQL
It describes and discusses various general methods of expressing constraints, eventually noting that support for "=" with relation operands is sufficient for completeness. It also notes that every constraint can be expressed as an invocation of IS_EMPTY, where IS_EMPTY(r) is equivalent to r { } = TABLE_DUM. First, though, it gives Example, showing how to use COUNT to test a relation for emptiness. Example here is a direct translation of that one into SQL.
Example: Testing for absence of counterexamples.
CREATE ASSERTION Must_be_enrolled_to_take_exam
CHECK ((SELECT COUNT (*)
FROM EXAM_MARK
WHERE (Student_Id, CourseId ) NOT IN
(SELECT Student_Id, CourseId
FROM IS_ENROLLED_ON ) )
= 0);
Using FOR UPDATE If you declare a cursor which will be referenced in the CURRENT OF clause of an UPDATE or DELETE statement, you should use the FOR UPDATE clause to obtain an
Selecting Objects: Suppose that you have run the SQL*Plus script below that creates object type Person and object table persons, and that you have settled the table: CREATE
Transaction Visibility As the figure shows, the changes made by an autonomous transaction become visible to another transaction whenever the autonomous transaction commits. Th
Disjunction (OR, ∨) Again we have nine rows instead of just four and again, when unknown is not involved, the rows are as for 2VL. Also, when anything is paired with true, t
i have an assignment of DBMS subject, this assignment is based on SQL server and power BI
Declaring Exceptions The Exceptions can be declared only in the declarative part of the PL/SQL subprogram, block, or package. By introducing its name, you can declare an excep
Fetching with a Cursor The FETCH statements retrieve the rows in the result set one at a time. After each and every fetch, the cursor advance to the next row in the result set
Overloading: Similar to packaged subprograms, methods of the same type can be overloaded. That is, you can use similar name for various methods if their formal parameters diff
Example of EXCEPT Operator - SQL Example, like its counterpart in the theory book, illustrates the convenience of allowing any table expression to be the source for an INSERT
Package STANDARD package named STANDARD defines the PL/SQL atmosphere. The package specification globally declares the exceptions, types, and subprograms that are available a
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