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Usefulness of Data Type
In SQL, as in most computer languages, a type can be used for constraining the values that are permitted to be used for some purpose. In particular, it can be used for constraining:
In each of the above cases, the type used for the purpose in question is the declared type of the variable, parameter, operator, or column, respectively. As a consequence, every expression denoting a value has a declared type too, whether that expression be a literal, a reference to a variable, parameter, or column, or an invocation of an operator. Thus SQL is able to detect errors at "compile time"- by mere inspection of a given script - that would otherwise arise, and cause much more inconvenience, at run time (when the script is executed).
WHEN or THEN Key Constraints Suppose a table has two columns representing a period of time throughout which the information conveyed by the other columns is recorded as having
EXIT Statement You can use the EXIT statement to exit a loop. The EXIT statement has 2 forms: the conditional EXIT WHEN and the unconditional EXIT. With the either form, you
Problem: (a) Define the following terms: (i) data mining. (ii) OLAP. (b) Differentiate between snowflake schema and star schema. Support your answer with appropriate
SQL Operators The PL/SQL uses all the SQL set, comparison, and row operators in the SQL statements. This part briefly describes some of these operators. 1. Comparison Opera
Updating Objects: To change the attributes of objects in an object table, you can use the UPDATE statement, as the illustration below shows: BEGIN UPDATE persons p SET p
Packaging Cursors You can split a cursor specification from its body for placement in a package. In that way, you can change the cursor body without changing the cursor spec
Using a Host Variable You can declare the cursor variable in the PL/SQL host environment like an OCI or Pro C program. To use the cursor variable, you should pass it as a host
Natural Join - SQL In the absence of NATURAL JOIN Example has to be replaced by something rather more longwinded, as shown in Example. Example: Joining IS_CALLED and IS_EN
Avoid the NOT NULL Constraint In the PL/SQL, using the NOT NULL constraint incur a performance cost. Consider the illustration as shown below: PROCEDURE calc_m IS m NUMB
Dynamic Ranges The PL/SQL lets you determine the loop range dynamically at run time, as the example below shows: SELECT COUNT(empno) INTO emp_count FROM emp; FOR i IN 1..emp_cou
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