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Effects of NULL
The numeric variable X, perhaps of type INTEGER, might be assigned NULL. In that case the result of evaluating X + 1 is NULL, and so SET Y = X + 1 assigns NULL to Y. A curious consequence of this is that immediately following this assignment the comparison Y = X + 1 does not evaluate to TRUE. For that matter, neither does the comparison Y = Y. In fact they both evaluate to UNKNOWN.
Grouping and Ungrouping in SQL Example specifying EXAM_MARK in place of COURSE in the main FROM clause. Example: Obtaining C_ER2 from EXAM_MARK SELECT CourseId, CAST
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
Deriving Predicates from Predicates in SQL The corresponding section in the theory book describes how predicates can be derived from predicates using (a) the logical connectiv
MERGE and TRUNCATE in SQL SQL has two more table update operators, MERGE and TRUNCATE. MERGE, like INSERT, takes a source table s and uses it to update a target table t. Brief
Parameter and Keyword Description: type_name: This identifies a user-defined type specifier that is used in the subsequent declarations of the objects. AUTHID Clause:
Extension and AND in SQL The theory book gives the following simple example of relational extension in Tutorial D: EXTEND IS_CALLED ADD ( FirstLetter ( Name ) AS Initial )
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
(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
Projection and Existential Quantification - SQL Intuitively it might seem that projection in SQL is simply a matter of specifying the required columns in the SELECT clause, a
Iteration Schemes The bounds of a loop range can be variables, literals, variables, or expressions but must compute to integers. Below are some of the examples. As you can see t
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