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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;
Definition of FROM - SQL Recall that the operand of FROM is denoted by a commalist, each element of that commalist being a table expression optionally accompanied by a range v
Example of UNWRAP Operator - SQL Example here shows how unwrapping can be done in longhand in SQL. Example: Unwrapping in SQL Letting CONTACT_INFO_WRAPPED denote the res
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Need Database Development with Analysis Tools Project Description: I want a database for large governmental and private data sets on one country that can be simply extended t
Inserting Objects: You can use the INSERT statement to add objects to an object table. In the illustration below, you insert a Person object into the object table persons:
Write an anonymous block that contains a PL/SQL procedure. The procedure takes two input parameter: oldZip and newZip, and it updates the zipcodes table by replacing all oldZip wit
Avoid the NOT NULL Constraint In the PL/SQL, using the NOT NULL constraint incur a performance cost. Consider the illustration as shown below: PROCEDURE calc_m IS m NUMB
Operator Precedence The operations within an expression are completed in a particular order depending on their precedence (priority). The table shows the default order of the op
Keyword and Parameter Description: label_name: This is an undeclared identifier which optionally labels the PL/SQL block. When used, label_name should be enclosed by the do
LONG and LONG RAW You use the LONG datatype to store the variable-length character strings. The LONG datatype is such as the VARCHAR2 datatype, except that the maximum length o
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