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SQL Database:
So, an SQL database is one whose symbols are organized into a collection of tables. Now, shows an SQL table as the current value of an SQL variable, ENROLMENT, but in that connection there are two important points to be made right away. First, the term table variable isn't used in SQL for its counterpart of relation variables. Instead, base relvars are normally referred to as base tables, virtual relvars as views (or viewed tables) and those terms are used in the international standard. Secondly, not every SQL table can be the value of a base table or view. As we shall soon see, table variables and the tables assigned to them are subject to several deviations from relational theory; tables that cannot be assigned to a variable are subject to even more deviations.
Data Abstraction The Data abstraction extracts the important properties of data while ignoring the not necessary details. Once you design a data structure, you can fail to reme
Using the Collection Methods The collection methods below help to generalize the code and make collections easier to use and also make your applications easier to maintain:
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
Logical Connectives - SQL SQL's extended truth tables in which the symbol, for unknown, appears along with the usual T and F. Negation (NOT, ¬) Conjunction (
Overloading The PL/SQL overloads the subprogram names. That is, you can use similar name for few different subprograms as long as their formal parameters differ in the number
Closest Approximation to Relational Union - SQL Actually, just as SQL has several varieties of JOIN, it also has several varieties of UNION, none of which is equivalent to th
PRIMARY KEY: PRIMARY KEY indicates that the table is subject to a key constraint, in this case declaring that no two rows in the table assigned to ENROLMENT can ever have the
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
Restriction and AND - SQL Restriction is available via the WHERE operator, and so it is in SQL. However, by Example showing how a certain simple restriction can be expressed u
Tautology - Equivalences Rules: If there Tautologies are not all the time as much easy to note as the one above so than we can use these truth tables to be definite that a sta
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