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CHECK Constraints in SQL
A CHECK constraint is a table constraint defined using the key word CHECK, as already illustrated in several examples in this chapter. In particular, a CHECK constraint can be used to express a constraint such as the one shown in Example, referred to in the theory book as a tuple constraint (so one might call it a row constraint in SQL). This is clearly the way most SQL users would prefer to express such a constraint.
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
Using LIMIT For nested tables, that have no maximum size, the LIMIT returns NULL. For varrays, the LIMIT returns the maximum number of elements that a varray can have (that yo
Stored Subprograms Normally, tools (like Oracle Forms) which incorporate the PL/SQL engine can store subprograms locally for later, strictly local execution. Though, to become
Using %TYPE The %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); debi
%NOTFOUND The %NOTFOUND is the logical opposite of the %FOUND. The %NOTFOUND yields TRUE when an INSERT, UPDATE, or DELETE statement affected no rows, or the SELECT INTO state
SELECT INTO Statement The SELECT INTO statement retrieve data from one or more database tables, and then assigns the selected values to the variables or fields. Syntax:
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
Mixed Notation The fourth procedure call shows that you can mix the positional and named notation. In this situation, the first parameter uses the positional notation, & the s
Advantages of PL/SQL The PL/SQL is a high-performance transaction processing, completely portable language that offers the following advantages as shown: 1) Support for SQL
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 )
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