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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.
Joining in SQL Joining IS_CALLED and IS_ENROLLED_ON in SQL SELECT * FROM IS_CALLED NATURAL JOIN IS_ENROLLED_ON This is an example of an SQL table expression. I have been
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
Name Resolution During the compilation, the PL/SQL compiler relates identifiers like the name of a variable with an address or memory location, actual value, or datatype. Th
PL SQL Code Review HEADER ELEMENTS File Name Clear, meaningful and descriptive about main objective of the file. Multiple words are joined using underscores which adh
Using Operator REF: You can retrieve refs by using the operator REF that, like VALUE, takes as its argument a correlation variable. In the illustration below, you retrieve one
Example of Shorthand for a row constraint Example: Shorthand for a row constraint ALTER TABLE EXAM_MARK ADD CONSTRAINT Mark_in_range CHECK (Mark BETWEEN 0 AND 100);
Row Counterparts of Table Operators SQL does not have counterparts tuple rename, tuple projection, tuple extension, tuple join and tuple compose. To obtain the same effects as
%FOUND Subsequent to a cursor or cursor variable is opened but before the first fetch, the %FOUND yields NULL. Afterward, it yields TRUE when the last fetch returned a row, or
Example of GROUP BY and COLLECT Operator Example: Using GROUP BY and COLLECT to obtain C_ER2 SELECT CourseId, CAST ( COLLECT (ROW (StudentId, Mark)) AS ROW (Studen
Explicit Cursors The set of rows returned by the query can include zero, one, or multiple rows, depending on how many rows meet your search criteria. Whenever a query returns
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