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Effects of NULL for UNIQUE Specification
When a UNIQUE specification u for base table t includes a column c that is not subject to a NOT NULL constraint, the appearance of several rows having NULL in place of a value for c and equal values for the other columns specified in u is permitted. It is only when each column of the specified "key" has a value that those column values may not appear in the same combination in more than one row of t.
Nested Tables versus Index-by Tables The Index-by tables and nested tables are just similar. For e.g. They have similar structure and their individual elements are accessed in
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
Effect of Anonymous Columns Now, recall that a VALUES expression denotes a table with undefined column names. If an initial value is to be specified when a base table is creat
UNNEST operator in SQL The inverse operator of GROUP is UNGROUP. SQL has an operator, UNNEST, that can be used for similar purposes, but its method of invocation is somewhat p
Avoiding Collection Exceptions In many cases, if you reference a nonexistent collection element, then PL/SQL raises a predefined exception. Consider the illustration shown b
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
Recursive Subprograms The recursive subprogram is the one that calls itself. Think of a recursive call as a call to a few other subprograms that does the similar task as your
FETCH Statement The FETCH statement retrieve rows of data one at a time from the result set of the multi-row query. The data is stored in fields or variables which correspond t
Package Body: The package specification is implemented by the package body. That is, the package body has the definition of every cursor and the subprogram declared in the pac
1. a. Write a trigger that fires when a part's price is updated. The trigger will write a record into a table called PriceUpdates. The record should contain the information of
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