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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 Cursor The Oracle implicitly opens a cursor to process each SQL statement not related with an explicit cursor. The PL/SQL refers to the most current implicit cursor as t
Case Sensitivity Similar to all the identifiers, the variables, the names of constants, and parameters are not case sensitive. For illustration, PL/SQL considers the following n
UNION and OR - SQL SQL supports UNION explicitly but differently from the way it supports JOIN explicitly. As we have seen, JOIN is used exclusively within the FROM clause, su
UTL_FILE: The Package UTL_FILE permits your PL/SQL programs to read & write operating system (OS) text files. It gives a restricted version of the standard OS stream file I/O,
Dynamic SQL: The Most PL/SQL programs do a predictable, specific job. For illustration, a stored procedure may accept an employee number and salary increase, and then update t
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Example of WHEN or THEN Constraints A concrete example showing how SQL supports WHEN/THEN constraints CREATE TABLE SAL_HISTORY (EmpNo CHAR (6), Salary INTEGER NOT NULL,
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Order of Evaluation When you do not use the parentheses to specify the order of evaluation, the operator precedence determine the order. Now compare the expressions below: NOT
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