Already have an account? Get multiple benefits of using own account!
Login in your account..!
Remember me
Don't have an account? Create your account in less than a minutes,
Forgot password? how can I recover my password now!
Enter right registered email to receive password!
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 evaluated against each row of the table t determined by the context in which the invocation appears. Then aggop considers only those rows that satisfy the condition x IS NOT NULL. It follows that if aggop is EVERY or SOME and x evaluates to TRUE or FALSE for at least one row of t, then the result is either TRUE or FALSE, never UNKNOWN. However, if x evaluates to UNKNOWN for every row of t (which is true in the particular case when t is empty), then SQL's other general rule kicks in, requiring the result to be NULL, which is equivalent to UNKNOWN when it appears in the place of a BOOLEAN value.
That anomaly is to some extent compensated for, when EVERY is used in constraint declarations, by SQL's rule that a constraint is deemed to be satisfied when it evaluates to UNKNOWN. However, (SELECT SOME(TRUE) FROM (tx) AS T) is not reliable as an existence test because it evaluates to UNKNOWN if the result of tx is empty, when a constraint based on that condition would be deemed satisfied. That problem could be addressed by writing COALESCE((SELECT SOME(TRUE) FROM (tx) AS T), FALSE) or, equivalently, (SELECT SOME(TRUE) FROM (tx) AS T) IS TRUE .
Declaring Exceptions The Exceptions can be declared only in the declarative part of the PL/SQL subprogram, block, or package. By introducing its name, you can declare an excep
Initializing and Referencing Collections Until you initialize a collection, a nested table or varray is automatically null (i.e. the collection itself is null, not its elements)
Definition of CROSS JOIN - SQL Let s = t1 CROSS JOIN t2, where t1 and t2 are table expressions optionally accompanied by range variables. Then: Note: Here T denotes Table
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
Existential Quantification - SQL Existential quantification-stating that something is true of at least one object under consideration-can be expressed by OR(r,c), meaning tha
Iterative Control: LOOP Statements The LOOP statement executes a series of statements multiple times. There are 3 forms of LOOP statements: LOOP, WHILE-LOOP, & FOR-LOOP. LOOP
UTL_FILE: The Package UTL_FILE permits your PL/SQL programs to read & write operating system (OS) text files. It gives a restricted version of the standard OS stream file I/O,
Processing Transactions This part describes how to do the transaction processing. You learn the fundamental techniques that safeguard the consistency of your database, involvin
Packaging Cursors You can split a cursor specification from its body for placement in a package. In that way, you can change the cursor body without changing the cursor spec
help
Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!
whatsapp: +91-977-207-8620
Phone: +91-977-207-8620
Email: [email protected]
All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd