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Name ResolutionIn potentially uncertain SQL statements, the names of the database columns take precedence over the names of the local variables and formal parameters. For e.g. the DELETE statement removes all the employees from the emp table, not just ’KING’, as Oracle suppose that both enames in the WHERE clause refer to thedatabase column:DECLAREename VARCHAR2(10) := ’KING’;BEGINDELETE FROM emp WHERE ename = ename;In such cases, to avoid the uncertainty, prefix the names of the local variables and formal parameters with my_, as shown below:DECLAREmy_ename VARCHAR2(10);Or, use a block label to qualify references, as in<>DECLAREename VARCHAR2(10) := ’KING’;BEGINDELETE FROM emp WHERE ename = main.ename;The next illustration shows that you can use a subprogram name to qualify references to a local variables and formal parameters:FUNCTION bonus (deptno IN NUMBER, ...) RETURN REAL ISjob CHAR(10);BEGINSELECT ... WHERE deptno = bonus.deptno AND job = bonus.job;
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
At times, customers make mistakes in submitting their orders and call to cancel the order. Brewbean’s wants to create a trigger that automatically updates the stock level of all pr
Effects of NULL in Aggregate Operator - SQL Let aggop(x) be an invocation of some aggregate operator aggop in SQL, where x is an expression (usually an open expression) to be
EXIT The EXIT statement forces a loop to done unconditionally. Whenever an EXIT statement is encountered, the loop is done immediately and controls the passes to the next statem
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 instea
Name Resolution In potentially uncertain SQL statements, the names of the database columns take precedence over the names of the local variables and formal parameters. For e.g.
%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:
Scoping Within the similar scope, all the declared identifiers should be unique. So, even if their datatypes differ, the variables and parameters cannot share the similar name.
Package STANDARD The package named STANDARD defines the PL/SQL atmosphere. The package specification globally declares the exceptions, types, and subprograms that are available
Positional and Named Notation You can write the actual parameters when calling a subprogram, using either positional or named notation. That is, you can point to the relationsh
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