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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.
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)
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
Table Comparison - SQL The following definitions for relation comparisons: Let r1 and r2 be relations having the same heading. Then: r1 ⊆ r2 is true if every tuple of r1
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
The Package Specification The package specifications contain the public declarations. The scopes of these declarations are local to your database representation and global to t
heap sort program in pl/sql
THEORY OF SPONTANEOUS GENERATION - ABIOGENESIS OR AUTOGENESIS - According to this theory, the existing living communities have originated from non-living organic matter with
Declarations in SQL Your program stores values in the variables and constants. As the program executes, the value of the variables can change, but the values constants cannot.
set serveroutput on declare a number(5); b number(5); c number(5); begin a:=&a; b:=&b; c:=a/b; dbms_output.put_line(c); exception when zero_divide then d
Logical Connectives - SQL SQL's extended truth tables in which the symbol, for unknown, appears along with the usual T and F. Negation (NOT, ¬) Conjunction (
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