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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.
Indeterminacy in SQL Some SQL expressions are actually not function invocations at all in the mathematical sense, being indeterminate-invocations operating on identical input
Data Types in SQL SQL's concept does not differ significantly from that defined in the theory book, apart from that business concerning NULL. However, the theory book equates
Assignment Source Not a Literal - Variable Syntax: SET SN = SID (SUBSTRING (SN.C FROM 1 FOR 1)||'5');
Example of NOT EXISTS in SQL Example: Use of NOT EXISTS CREATE ASSERTION Must_be_enrolled_to_take_exam_alternative1 CHECK ( NOT EXISTS (SELECT StudentId, CourseId
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
Keyword and Parameter Description select_statement: This is a query which returns a result set of the rows. Its syntax is such that of select_ into_statement without the IN
IN Operator The operator IN tests the set membership. This means "equal to any member of." The set may have nulls, but they are ignored. For illustration, the statement below do
Parameter SELF in pl/sql The MEMBER methods recognize a built-in parameter named SELF that is an instance of the object type. Whether declared explicitly or implicitly, it is
Naming Conventions The similar naming conventions apply to all PL/SQL program items and units including the variables, cursors, constants, cursor variables, procedures, exception
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