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WHILE-LOOPThe WHILE-LOOP statement relates a condition with the series of statements enclosed by the keywords LOOP and END LOOP, as shown:WHILE condition LOOPsequence_of_statementsEND LOOP;Before each of the iteration of the loop, the condition is computed. If the condition is true, then the series of statements is executed, then the control resumes at the top of the loop. When the condition is false or null, the loop is then bypassed and control passes to the next statement. An illustration is shown below:WHILE total <= 25000 LOOP...SELECT sal INTO salary FROM emp WHERE...total := total + salary;END LOOP;The number of iterations depends on the condition and is not known until the loop done. The condition is tested at the top of the loop, so the series might execute zero times. In the last illustration, if the initial value of total is bigger than 25000, the condition is false and the loop is bypassed.A few languages have a LOOP UNTIL or REPEAT UNTIL structure, that tests the condition at the bottom of the loop rather than at the top. So, the sequence of the statements is executed at least once. The PL/SQL has no such structure, but you can easily build one, as shown:LOOPsequence_of_statementsEXIT WHEN boolean_expression;END LOOP;To make sure that a WHILE loop executes at least once, then use an initialized Boolean variable in the condition which is as shown below:done := FALSE;WHILE NOT done LOOPsequence_of_statementsdone := boolean_expression;END LOOP;The statement inside the loop should assign a new value to the Boolean variable. Or else, you have an infinite loop. For illustration, the following LOOP statements are logically equal:WHILE TRUE LOOP | LOOP... | ...END LOOP; | END LOOP;
Parameter Aliasing To optimize the subprogram call, the PL/SQL compiler can decide between the two techniques of the parameter passing. With the by-value techniques, the v
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.
Parameter and Keyword Description: record_type_name: This identifies the user-defined type specifier that is used in the subsequent declarations of the records. NOT N
(a) What are decision support systems, and what role do they play in the business environment? (b) Data warehousing is defined as "a subject-oriented, integrated, non-volatile c
GOTO Statement The GOTO statement branches to a label unconditionally. The label must be exclusive within its scope and should precede an executable statement or a PL/SQL block.
Effects of NULL for Table Expression Here's an important distinction between expressions denoting tables and expressions denoting multisets of rows: a table expression cannot
Example of WRAP Operator - SQL The effect of Example can be obtained in SQL but note that one needs to write down not only the names of the columns being wrapped but also the
Aggregate Assignment The %ROWTYPE declaration cannot include an initialization clause. Though, there are two ways to assign values to all fields in a record at once. At First, t
Parameter Modes To define the behavior of formal parameters you use the parameter modes. The 3 parameter modes, IN, OUT, & IN OUT, can be used with any subprogram. Though, a
Table Comparison - SQL The following definitions for relation comparisons: Let r1 and r2 be relations having the same heading. Then: r1 ⊆ r2 is true if every tuple of r1
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