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Variable Declaration - SQL
SQL's support for variables is very similar to Tutorial D's, except that the syntax for creating persistent variables-base tables-is quite different from that used to declare local variables. Example is SQL's counterpart of that example in the theory book but, as you know, CREATE TABLE is used for base tables.
Example: A Variable Declaration
DECLARE SN SID DEFAULT SID ('S1');
DECLARE in place of VAR and DEFAULT in place of INIT. The effect is exactly the same apart from the fact that, as already noted, SQL's type SID (here assumed to be a distinct type). The key word DEFAULT is perhaps a strange choice as that word normally suggests action to be taken by the system when no specific action is explicitly demanded by the user. Here it is used to state explicitly an immediate assignment to the variable being declared.
IN Operator The operator IN tests the set membership. This means "equal to any member of." The set may have nulls, but they are ignored. For illustration, the statement below do
First Step at defining type SID in SQL CREATE TYPE SID AS ( C VARCHAR(5) ) ; Explanation: TYPE SID announces that a type named SID is being defined to the syst
IF Statement The IF statement executes a series of statement conditionally. Whether the series is executed or not depends on the value of the Boolean expression. Syntax:
Predicate - SQL Consider the declarative sentence-a proposition-that is used to introduce this topic: "Student S1, named Anne, is enrolled on course C1." Recall that th
Closest Approximation to Relational Union - SQL Actually, just as SQL has several varieties of JOIN, it also has several varieties of UNION, none of which is equivalent to th
LOOP Statements The LOOP statements execute a series of statements at multiple times. The loops enclose the series of statements that is to be repeated. The PL/SQL provides typ
%ISOPEN The %ISOPEN yields TRUE if its cursor or cursor variable is open; or else, the %ISOPEN yields FALSE. In the illustration, you use the %ISOPEN to select an action:
Keys in SQL SQL support for keys in the following respects: SQL does not require at least one key for every base table. If no key is explicitly declared, then KEY {ALL B
Parameter and Keyword Description: label_name: This is an undeclared identifier which optionally labels a loop. When used, the label_name should be enclosed by double ang
Parameter and Keyword Description: table_reference: This keyword identifies the table or view that should be accessible when you execute the UPDATE statement, and for wh
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