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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.
Error Handling The PL/SQL makes it easy to detect and process the predefined and user-defined error conditions known as exceptions. Whenever an error occurs, an exception is ra
Closing a Cursor The CLOSE statements disable the cursor, and the result set becomes undefined. An illustration of the CLOSE statement as shown: CLOSE c1;
Subprograms The PL/SQL has two types of subprograms known as the procedures and functions that can take parameters and be invoked. As the following example represents, a subp
Collections: The collection is an ordered group of elements, all of similar type (for illustration, the grades for a class of students). Each element has an exclusive subsc
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:
Declaring Cursor Variables Once a REF CURSOR type is define by you, and then you can declare the cursor variables of that type in any PL/SQL block or subprogram. In the exampl
Example of UNWRAP Operator - SQL Example here shows how unwrapping can be done in longhand in SQL. Example: Unwrapping in SQL Letting CONTACT_INFO_WRAPPED denote the res
Cursor FOR Loops In most cases that need an explicit cursor, you can simplify the coding by using a cursor FOR loop rather of the OPEN, FETCH, and CLOSE statements. A cursor FO
Scope and Visibility The References to an identifier are resolved according to its visibility and scope. The scope of an identifier is that area of a program unit (subprogram, b
Using the BULK COLLECT Clause The keywords BULK COLLECT specify the SQL engine to bulk-bind output collections before returning them to the PL/SQL engine. You can use these ke
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