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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.
UPDATE Command- SQL Loosely speaking, UPDATE changes some of the column values of some existing rows of its target table. Thus, although some rows disappear from the target an
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
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 Suppose the university decides that course C3 is to be withdrawn.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
Example of GROUPBY Operator Example: How many students sat each exam, using GROUP BY, NATURAL LEFT JOIN, and COALESCE SELECT CourseId, COALESCE (n, 0) AS n FROM COURS
Main features of PL/SQL A good way to get familiar with PL/SQL is to look at a sample program. The below program processes an order for tennis rackets. At first, it declares a
Functions The function is a subprogram that calculates a value. The Functions and procedures are structured similar, except that the functions have a RETURN clause. You can
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
UTL_FILE: The Package UTL_FILE permits your PL/SQL programs to read & write operating system (OS) text files. It gives a restricted version of the standard OS stream file I/O,
to write a heap sort program usin pl-sql
JOIN and AND in SQL In this Section is all about one operator, JOIN. SQL's closest counterpart, NATURAL JOIN, has already been covered. Here we look at several other "join" op
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