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Using %TYPEThe %TYPE attribute gives the datatype of a variable or the database column. In the example below, the %TYPE gives the datatype of a variable:credit REAL(7,2);debit credit%TYPE;The Variables declared using %TYPE is treated such as those declared using a datatype specifier. For example, given the earlier declarations, the PL/SQL treats debit such as REAL (7, 2) variable. The later example shows that a %TYPE declaration can involve an initialization clause:balance NUMBER(7,2);minimum_balance balance%TYPE := 10.00;The %TYPE attribute is mainly useful when declaring a variable which refer to a database columns. You can reference a table & column, or you can reference an owner, column, table, and as inmy_dname scott.dept.dname%TYPE;Using the %TYPE to declare my_dname has two merits. Firstly, you do not require knowing the exact datatype of dname. Secondly, when the database definition of the dname changes, the datatype of my_dname change accordingly at the run time.
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
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 )
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
Example of DELETE - SQL As with UPDATE, a FOR PORTION OF clause can be specified if the target table has a defined period name, as illustrated in Example. Example: Deleting
Expressions An expression is a randomly complex combination of the constants, variables, literals, operators, & function calls. The simplest expression is the single variabl
Using Aliases The Select-list items fetched from a cursor related with the %ROWTYPE should have simple names or, if they are expressions, should have aliases. In the example bel
JOIN and AND in SQL In this Section is all about one operator, JOIN. SQL's closest counterpart, NATURAL JOIN, has already been covered. Here we look at several other "join" op
Important Distinctions The list of important distinctions are given below: Value versus variable Syntax versus semantics Variable versus variable reference
Write a query to find academics that are authors and that have only ever coauthored papers with authors from institutes in the same state as their own. List their academic number,
Using LOCK TABLE You use the LOCK TABLE statement to lock the whole database tables in the specified lock mode so that you can share or deny the access to them. For illustrati
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