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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;
EXIT-WHEN The EXIT-WHEN statement permits a loop to complete conditionally. Whenever the EXIT statement is encountered, the condition in the WHEN clause is computed. When the co
Updating Objects: To change the attributes of objects in an object table, you can use the UPDATE statement, as the illustration below shows: BEGIN UPDATE persons p SET p
I need a query for PL/SQL, selecting names with cursor, goes down the list, assigns usernames (initials001) based on initials in the name. If two names have same initials the user
Assignment Source Not a Literal - Variable Syntax: SET SN = SID (SUBSTRING (SN.C FROM 1 FOR 1)||'5');
I have a Pascal Source file that needs to be compiled into a Service. In addition, there are various functions (Pascal Procedures I guess) that need to be created to Read and Write
Effects of NULL for Multiple Assignments - SQL If the row expression given as the source for a multiple assignment evaluates to NULL, then NULL is assigned to each target. If
UNNEST operator in SQL The inverse operator of GROUP is UNGROUP. SQL has an operator, UNNEST, that can be used for similar purposes, but its method of invocation is somewhat p
Using Cursor Attributes To process the SQL data manipulation statements, the SQL engine must opens an implicit cursor named SQL. This cursor's attributes (%FOUND, %NOTFOUND, %
FETCH Statement The FETCH statement retrieve rows of data one at a time from the result set of the multi-row query. The data is stored in fields or variables which correspond t
Keyword & Parameter Description: PRAGMA: These keywords signify that the statement is a pragma (i.e. compiler directive). The Pragmas are processed at the compile time, n
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