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Semidifference and NOT - SQL
In this section first describe the relational difference operator, named MINUS. Example here shows SQL's closest counterpart of that operator.
Example: Difference in SQL
SELECT StudentId
FROM IS_CALLED
WHERE Name = 'Devinder'
EXCEPT DISTINCT CORRESPONDING
FROM IS_ENROLLED_ON
WHERE CourseId = 'C1'
The syntax for EXCEPT exactly parallels that for UNION. The key words DISTINCT, ALL, and CORRESPONDING have exactly the same significance as in UNION, and DISTINCT remains the default option. When CORRESPONDING is not given, columns are paired by ordinal position, as in UNION.
Example of Alternative formulation as a table constraint Example: Alternative formulation as a table constraint ALTER TABLE EXAM_MARK ADD CONSTRAINT Must_be_enrolled_to_
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
Order of Evaluation When you do not use the parentheses to specify the order of evaluation, the operator precedence determine the order. Now compare the expressions below: NOT
SELECT INTO Statement The SELECT INTO statement retrieve data from one or more database tables, and then assigns the selected values to the variables or fields. Syntax:
Defining and Declaring Records To create records, you have to define a RECORD type, and then declare records of that type. You may also define RECORD types in the declarative
INSERT Statement The INSERT statement adds fresh rows of data to the specified database table or view. Syntax:
Collections: The collection is an ordered group of elements, all of similar type (for illustration, the grades for a class of students). Each element has an exclusive subsc
Exceptions An exception is the runtime error or warning condition that can be predefined or user-defined. The Predefined exceptions are raised implicitly through runtime system
When Are Constraints Checked Under the model constraints are conceptually checked at all statement boundaries (and only at statement boundaries). By default the same is true
Loop Labels Like the PL/SQL blocks, loops can also be labeled. The label, an undeclared identifier enclosed by double angle brackets, should appear at the beginning of the LOOP
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