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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.
SQL Pseudocolumns The PL/SQL recognizes the following SQL pseudocolumns, that returns the specific data items: LEVEL, NEXTVAL, CURRVAL, ROWID, & ROWNUM. The Pseudocolumns are n
"Not Enforced" Table Constraints A constraint that is not enforced is not really a constraint within the meaning of the act, but SQL does have such a concept and it needs to b
Parameter Modes: You do not require to specify a parameter mode for the input bind arguments (those used, for illustration, in the WHERE clause) as the mode defaults to IN. Th
Operators on Tables and Rows Row Extraction TUPLE FROM r, SQL has row subqueries. These are just like scalar subqueries except that they may specify more than one column.
Adding Table Constraints ALTER TABLE ENROLMENT ADD CONSTRAINT NameNotNull CHECK (Name IS NOT NULL) ; ALTER TABLE ENROLMENT ADD CONSTRAINT PK_StudentId_CourseId PRIM
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,
DELETE Statement The DELETE statement eliminates whole rows of data from the specified table or view. 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
Fetching Across Commits The FOR UPDATE clauses acquire exclusive all row locks. All rows are locked when you open the cursor, and when you commit your transaction they are unl
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 sev
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