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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.
Example of Using Aggregation on Nested Tables Example: How many students sat each exam WITH C_ER AS (SELECT CourseId, CAST (TABLE (SELECT DISTINCT StudentId, Mark FROM EXAM
Row Operators The Row operators return or reference the particular rows. ALL retains the duplicate rows in the result of a query or in an aggregate expression. The DISTINCT el
UPDATE Statement The UPDATE statement transforms the values of the specified columns in one or more rows in the table or view. Syntax:
Declarations in SQL Your program stores values in the variables and constants. As the program executes, the value of the variables can change, but the values constants cannot.
Advantages of Wrapping The PL/SQL Wrapper convert the PL/SQL source code into a transitional form of the object code. By hiding the application internals, the Wrapper secure
Query: SELECT * FROM EMPLOYEE1; Select 5 columns and all rows from one table Query: SELECT C_ID, COMPANY, BUILDING, DEPARTMENT, BRANCH FROM CONTRACT;
Pl/sql Conditional Control: IF statements Frequently, it is necessary to take the alternative actions depending on the circumstances. The IF statement execute a series of statem
EXECUTE IMMEDIATE Statement The EXECUTE IMMEDIATE statement prepare (parses) and instantly executes a dynamic SQL statement or an anonymous PL/SQL block. Syntax:
Controlling Autonomous Transactions The first SQL statement in an autonomous routine starts a transaction. Whenever one transaction ends, the next SQL statement starts the oth
Map and Order Methods: The values of the scalar datatype like CHAR or REAL have a predefined order that allows them to be compared. While, the instances of an object type has
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