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SQL Is a Database Language:
The commands given to a DBMS by an application are written in the database language of the DBMS. The term data sublanguage is sometimes used instead of database language. The sub- prefix refers to the fact that application programs are sometimes written in some more general-purpose programming language (the "host" language), in which the database language commands are embedded in some prescribed style. Sometimes the embedding style is such that the embedded statements are unrecognized by the host language compiler or interpreter, and some special preprocessor is used to replace the embedded statements by, for example, CALL statements in the host language.Those remarks apply to SQL, as does the remainder of that section. Moreover, Part 10 of the international standard for SQL defines classes for use in object-oriented languages, in particular, Java, thus allowing method invocations to be used in place of old-fashioned CALL statements.
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
Example of Foreign Key Constraint Example: Alternative formulation for 6.3 as a foreign key constraint ALTER TABLE EXAM_MARK ADD CONSTRAINT Must_be_enrolled_to_take_exam
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
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
Using Cursor Attributes: Every cursor has 4 attributes: %NOTFOUND, %FOUND, %ISOPEN, and %ROWCOUNT. If appended to the cursor name, they return the helpful information about
Projection in SQL - correct version Student StudentId is enrolled on some course. SELECT DISTINCT StudentId FROM IS_ENROLLED_ON In more complicated examples it is someti
Using NOT NULL Besides assigning an initial value, the declarations can impose the NOT NULL constraint, as the example below shows: acct_id INTEGER(4) NOT NULL := 9999; You ca
Initializing Records The illustration below shows that you can initialize a record in its type definition. Whenever you declare a record of the type TimeRec, its 3 fields supp
Autonomous versus Nested Transactions Though an autonomous transaction is started by the other transaction, it is not a nested transaction for the reasons shown below: (i)
UNION ALL - SQL Further varieties of UNION arise when we replace the key word DISTINCT by ALL in any of the foregoing examples, as in Example. ALL specifies that if row r appe
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