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MAX and MIN operator in SQL
Example:
(SELECT MAX (Mark) FROM EXAM_MARK WHERE StudentId = 'S1')
(SELECT MIN (Mark) FROM EXAM_MARK WHERE StudentId = 'S1')
Example needs no further explanation. SQL also has AVG for averages. Its counterparts aggregate AND and OR are spelled, respectively, EVERY and either SOME or ANY, but all of these must be used with care because of the consequences of the aforementioned general rule concerning the treatment of NULL. For example, if the condition c evaluates to UNKNOWN for every row of table t, or t is empty, then (SELECT EVERY(c) FROM t) evaluates to UNKNOWN, whereas when t is empty it really ought to evaluate to TRUE.
Manipulating Collections Within PL/SQL, the collections add procedural power and flexibility. The biggest benefit is that your program can compute subscripts to process the spec
Example of COALESCE operator Example: Give the total of marks for each exam (simplified solution) SELECT CourseId, COALESCE ((SELECT SUM (Mark) FROM EXAM_MARK AS EM
Manipulating Local Collections Within PL/SQL, to manipulate the local collection, by using the TABLE and CAST operators . The operands of CAST are a collection declared locally
UNION and OR - SQL SQL supports UNION explicitly but differently from the way it supports JOIN explicitly. As we have seen, JOIN is used exclusively within the FROM clause, su
Left and Right Joins LEFT OUTER JOIN can be used when you want to retrieve the data from the main table (table1) even if there is no match in other tables (table_2, table_3...
Projection in SQL - correct version Student StudentId is enrolled on some course. SELECT DISTINCT StudentId FROM IS_ENROLLED_ON In more complicated examples it is someti
ROWNUM The ROWNUM returns a number representing the order in which a row was selected from the table. The first row selected has a ROWNUM of 1; the second row has a ROWNUM of
Quantification in SQL To quantify something, as the theory book has it, is to state its quantity, to say how many of it there are. For example, in Tutorial D the expression CO
OPEN-FOR Statement The OPEN-FOR statements execute the multi-row query related with a cursor variable. It also allocates the resources used by the Oracle to process the query a
Semijoin and Composition - SQL For semijoin, the dyadic relational operator MATCHING, defined thus: r1 MATCHING r2, where r1 and r2 are relations such that r1 JOIN r2 is de
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