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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, such that IS_CALLED NATURAL JOIN IS_ENROLLED_ON, for example, can be an element of that clause but cannot stand alone as a table expression. Instead, UNION always connects table expressions that can stand alone, these being:
Iterative Control: LOOP Statements The LOOP statement executes a series of statements multiple times. There are 3 forms of LOOP statements: LOOP, WHILE-LOOP, & FOR-LOOP. LOOP
Tautology - Equivalences Rules: If there Tautologies are not all the time as much easy to note as the one above so than we can use these truth tables to be definite that a sta
Example of Check Constraints Example: Workaround for when subqueries not permitted in CHECK constraints CREATE FUNCTION NO_MORE_THAN_20000_ENROLMENTS ( ) RETURNS BOOLEAN
Scoping Within the similar scope, all the declared identifiers should be unique. So, even if their datatypes differ, the variables and parameters cannot share the similar name.
Enrolment was split - SQL Example shows how relvars IS_CALLED and IS_ENROLLED_ON can be derived from the original ENROLMENT relvar, using projection in the initial assignment
Assignment Source Not a Literal - Variable Syntax: SET SN = SID (SUBSTRING (SN.C FROM 1 FOR 1)||'5');
Short-Circuit Evaluation When computing a logical expression, the PL/SQL uses short-circuit evaluation. That is, the PL/SQL stops computing the expression as soon as the result
Declaring Objects: You can use the object types wherever built-in types like CHAR or NUMBER can be used. In the block below, you can declare object r of type Rational. Then, yo
Example of Cast Operator So long as CAST is used as shown, we could obtain the total marks for each exam in similar fashion, using SUM (Mark) AS TotalMarks. However, this giv
Collection Methods: The collection method is a built-in function or procedure which operates on the collections and is called using the dot notation. The methods like the C
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