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IN OperatorThe operator IN tests the set membership. This means "equal to any member of." The set may have nulls, but they are ignored. For illustration, the statement below does not delete the rows in which the ename column is null:DELETE FROM emp WHERE ename IN (NULL, ’KING’, ’FORD’);Moreover, the expressions of the formvalue NOT IN setyield FALSE when the set contains a null. For illustration, instead of deleting the rows in which the ename column is not null and not ’KING’, the statement below deletes no rows:DELETE FROM emp WHERE ename NOT IN (NULL, ’KING’);Concatenation OperatorThe Double vertical bars (||) serve as the concatenation operator that appends one string to another. For illustration, the expression’suit’ || ’case’returns the value as shown below:’suitcase’If both the operands have datatype CHAR, the concatenation operator returns a CHAR value. Or else, it returns a VARCHAR2 value.
Providing Results of Queries Expressing queries in SQL is the (big) subject. Here I present just a simple example to give you the flavour of things to come in those chapters.
Recursion versus Iteration Dissimilar the iteration, recursion is not crucial to PL/SQL programming. Any problem which can be solved using recursion can be solving using the it
Effects of NULL Operator As a general rule-but not a universal one-if NULL is an argument to an invocation of a system-defined read-only operator, then NULL is the result of t
Example of NOT EXISTS in SQL Example: Use of NOT EXISTS CREATE ASSERTION Must_be_enrolled_to_take_exam_alternative1 CHECK ( NOT EXISTS (SELECT StudentId, CourseId
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 Suppose the university decides that course C3 is to be withdrawn.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
Using Host Arrays The Client-side programs can use anonymous PL/SQL blocks to bulk-bind input and output host arrays. However, this is the well-organized way to pass the colle
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
Bulk Fetching The illustration below shows that you can bulk-fetch from a cursor into one or more collections: DECLARE TYPE NameTab IS TABLE OF emp.ename%TYPE; TYPE S
Deriving Predicates from Predicates in SQL The corresponding section in the theory book describes how predicates can be derived from predicates using (a) the logical connectiv
Define basic operators of relational algebra with an example each
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