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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.
Natural Join - SQL In the absence of NATURAL JOIN Example has to be replaced by something rather more longwinded, as shown in Example. Example: Joining IS_CALLED and IS_EN
NULL Statement The NULL statement clearly specifies in action; it does nothing other than to pass control to the next statement. It can, though, improve the readability. In a
Logical Connectives - SQL SQL's extended truth tables in which the symbol, for unknown, appears along with the usual T and F. Negation (NOT, ¬) Conjunction (
Using EXISTS The EXISTS(n) returns TRUE if the nth element in a collection exist. Or else, EXISTS(n) returns FALSE. Primarily, you use EXISTS with DELETE to maintain the spars
Keyword and Parameter Description: table_reference: This specifies a table or view that should be accessible when you execute the DELETE statement, and for that you must
DELETE Statement The DELETE statement eliminates whole rows of data from the specified table or view. Syntax:
Advantages of Subprograms The Subprograms give extensibility; that is, tailor the PL/SQL language to suit your requirements. For illustration, if you require a procedure which
Row Counterparts of Table Operators SQL does not have counterparts tuple rename, tuple projection, tuple extension, tuple join and tuple compose. To obtain the same effects as
Advantages of Invoker Rights The Invoker-rights routines centralize the data retrieval. They are particularly helpful in applications which store data in various schemas. In su
Operators on Tables and Rows Row Extraction TUPLE FROM r, SQL has row subqueries. These are just like scalar subqueries except that they may specify more than one column.
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