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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.
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:
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Identifiers You use identifiers to name the PL/SQL program items and units that include constants, variables, cursors, exceptions, cursor variables, subprograms, and packages.
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