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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.
Fetching Across Commits The FOR UPDATE clauses acquire exclusive all row locks. All rows are locked when you open the cursor, and when you commit your transaction they are unl
Primary Key - SQL A PRIMARY KEY specification carries an implicit NOT NULL constraint on each column of the specified key. When more than one key constraint is required, the k
Parameter and Keyword Description: table_reference: This keyword identifies the table or view that should be accessible when you execute the UPDATE statement, and for wh
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
which operation is used if we are interested in only certain columns of a table?
Parameter & Keyword Description: function_name: The user-defined function is identifying by that keyword. parameter_name: This identifies the formal parameter that
Effects of NULL The numeric variable X, perhaps of type INTEGER, might be assigned NULL. In that case the result of evaluating X + 1 is NULL, and so SET Y = X + 1 assigns NULL
Fetching from a Cursor Variable The FETCH statement retrieve rows one at a time from the product set of a multi-row query. The syntax for the same is as shown: FETCH {curso
Updating by replacement Syntax: UPDATE ENROLMENT SET Name = 'Ann' WHERE StudentId = SID ('S1'); Note the use of SET, as already noted in connection with direct a
EXECUTE IMMEDIATE Statement The EXECUTE IMMEDIATE statement prepare (parses) and instantly executes a dynamic SQL statement or an anonymous PL/SQL block. Syntax:
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