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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 Subqueries A subquery is a query (typically enclosed by parentheses) that appears within another SQL data manipulation statement. If evaluated, the subquery gives a va
Delimiters A delimiter is a simple or compound symbol which has a special meaning to PL/SQL. For example, you use delimiters to symbolize an arithmetic operation like additio
%TYPE Attribute The %TYPE attribute gives the datatype of a record, field, nested table, database column, or the variable. You can use the %TYPE attribute as the datatype speci
1- You can check attribute names from each table in DBF11 by running for example: desc dbf11.Member; desc dbf11.Agent; desc dbf11.Producer; Because some attribute names in
Parameter and Keyword Description: package_name: This construct identifies the package. AUTHID Clause: This determine whether all the packaged subprograms impleme
Referencing Records Unlike the elements in a collection, that are accessed using subscripts, the fields in a record are accessed by name. To reference an individual field, you
Information Hiding With the information hiding, you see only the details that are significant at a given level of algorithm and data structure design. The Information hiding
%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
Overriding Default Locking By default, the Oracle locks the data structures for you automatically. Though, you can request exact data locks on rows or tables when it is to you
INSERT Statement The INSERT statement adds fresh rows of data to the specified database table or view. Syntax:
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