expressly disclaim all warranties of any kind with respect to third-party content, products, and services . Relational Database Management System (RDBMS). The most popular RDBMS are MS SQL Server, DB2, Oracle and MySQL. PROPERTY of the database whereas the RDBMS is more with this regard because. Describe the Oracle implementation of the RDBMS and ORDBMS. Describe new The user interacts with DBMS and not with the database. The primary.
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Dependency Preservation, Lossless design, Comparison of Oracle & DB2. . In turn, all programs that access the data in the database work through the DBMS. management system (RDBMS) and the object relational database management SQL Statements. Oracle SQL complies with industry-accepted standards. Oracle RDBMS & SQL Tutorial (Very Good) - Free download as PDF File In relational database systems (DBS) data are represented using tables (relations).
A foreign key is an important attribute of a relation which should be referred to in other relationships. Referential integrity constraint state happens where relation refers to a key attribute of a different or same relation. However, that key element must exist in the table. Example: In the above example, we have 2 relations, Customer and Billing. Insert is used to insert data into the relation Delete is used to delete tuples from the table.
Modify allows you to change the values of some attributes in existing tuples. Select allows you to choose a specific range of data. Whenever one of these operations are applied, integrity constraints specified on the relational database schema must never be violated.
Inset Operation The insert operation gives values of the attribute for a new tuple which should be inserted into a relation.
Delete Operation To specify deletion, a condition on the attributes of the relation selects the tuple to be deleted. The Delete operation could violate referential integrity if the tuple which is deleted is referenced by foreign keys from other tuples in the same database.
For example.. Together with this operator. To test for inequality. In contrast. If m is not specified. A powerful operator for pattern matching is the like operator.
List the job title and the salary of those employees whose manager has the number or and who earn more than Further string operations are: For all data types. Further comparison operators are: They are used to compute a single value from a set of attribute values of a column: How many tuples are stored in the relation EMP?
List the minimum and maximum salary. For each column. There is no difference between names in lower case letters and names in upper case letters. In fact.. How many different job titles are stored in the relation EMP? Column definitions are separated by colons. A not null 6. Compute the difference between the minimum and maximum salary..
Sum of all salaries of employees working in the department MGR number 4. ENAME varchar2 30 not null. SAL number 7. JOB varchar2 In this section we consider only very simple constraints. More complex constraints will be discussed in Section 5.
Based on a primary key. It is advisable to name a constraint in order to get more meaningful information when this constraint is violated due to. A primary key constraint enables a unique identification of each tuple in a table. Unless the condition not null is also specified for this column. Probably the most important type of integrity constraints in a database are primary key con- straints.
The two most simple types of constraints have already been discussed: If no name is specified for the constraint. Basically two types of constraints are provided: The specification of a simple constraint has the following form: The keyword unique specifies that no two tuples can have the same attribute value for this column.
Table definition: If it is required. Note that in contrast to a unique constraint. A primary key constraint that includes more than only one column can be specified in an analogous way.
A unique constraint can include more than one attribute. For this. PMGR number 4 not null. For each project. A table.. Instead of a not null constraint it is sometimes useful to specify a default value for an attribute if no value is given.
PNAME varchar2 60 unique. PEND date. Unlike integrity constraints. Suppose we have defined the following table: Thus an insertion does not necessarily have to follow the order of the attributes as specified in the create table statement.
If there are already some data in other tables. For each of the listed columns. What are the data types of the attributes? Should varchar2 be used instead of char? Which columns do not allow duplicates?
If a column is omitted. If no column list is given. All salesmen working in the department 20 get the same salary as the manager who has the lowest salary among all managers. Analogous to the insert statement. An expression consists of either a constant new value. This value then is assigned to all salesmen working in department HDATE date. We now can use the table EMP to insert tuples into this new relation: An update statement without a where clause results in changing respective attributes of all tuples in the specified table.
The query retrieves the minimum salary of all managers. As long as the user has not issued the commit statement. A commit is also implicitly executed when the user terminates an Oracle session. They become permanent only after the statement commit. Modifications of tuples are temporarily stored in the database system. Another important SQL function is user. It is important that the order of data types and values of the selected row exactly correspond to the list of columns in the set clause. It is also possible to specify a query that retrieves more than only one value but still only one tuple!
A major feature of relational databases. Note that any data definition command such as create table results in an internal commit. To undo modifications.
If the where clause is omitted. It is advisable to complete each modification of the database with a commit as long as the modification has the expected effect. In SQL the select statement is used for this kind of queries joining relations: Delete all projects tuples that have been finished before the actual date system date: DEPT D.
For each salesman. The columns compared by this operator are called join columns and the join operation is called an equijoin. If we want to refer to either of these columns in the where or select clause. Any number of tables can be combined in a select statement. MGR and D. The computation of the query result occurs in the following manner without optimization: From these rows those that have the same department number are selected where E.
Instead of a table alias also the complete relation name can be put in front of the column such as DEPT. In the table EMP only the numbers of the departments are stored. A query result can also be used in a condition of a where clause. The subquery retrieves the set of those employees who manage a project that started before December If the employee working in department 20 is contained in this set in operator.
A respective condition in the where clause then can have one of the following forms: As we have already seen for the insert statement. EMP E2 where E1. The equijoin comparison is E1. It is even possible to join a table with itself: List the names of all employees together with the name of their manager: List the name and salary of employees of the department 20 who are leading a project that started before December In such a case the query is called a subquery and the complete select statement is called a nested query.
Retrieve all employees who are working in department 10 and who earn at least as much as any i. If the subquery yields an empty result set. An important class of subqueries are those that refer to its surrounding sub query and the tables listed in the from clause. A subquery may use again a subquery in its where clause. Note that an alias for the table EMP in the subquery is not necessary since columns without a preceding alias listed there always refer to the innermost query and tables.
The subquery in this example is related to its surrounding query since it refers to the column E1. Such type of queries is called correlated subqueries.
The subquery retrieves only one value the number of the department located in Boston. As long as the result of a subquery is not known in advance. One can think of the evaluation of this query as follows: For each tuple in the table E1.
List all those employees who are working in the same department as their manager note that components in [ ] are optional: Thus conditions can be nested arbitrarily.. In this case the condition evaluates to true if the subquery does not yield any row or value. List all departments that have no employees: For each tuple from the table DEPT. SQL supports three set operators which have the pattern: If there exists a corresponding tuple in the table EMP.
List all employees who are not working in department 30 and who earn more than all employees working in department Such type of queries is formulated using the exists operator. In case no such tuple exists. Duplicates are automatically eliminated unless the clause all is used.
Also in this subquery no aliases are necessary since the columns refer to the innermost from clause. For all and any. For each department.
Rows from the table EMP are grouped such that all rows in a group have the same department number. Each operator requires that both tables have the same data types for the columns to which the operator is applied.
This clause appears after the where clause and must refer to columns of tables listed in the from clause. We thus get the following query result: The aggregate functions are then applied to each such group. Often applications require grouping rows that have certain properties and then applying an aggregate function on one column for each group separately.
Aggregations specified in the select clause are then applied to each group sepa- rately. In the above query.
Note that it is even possible to specify a subquery in a having clause. This type of condition is specified using the having clause. Retrieve values for the columns and aggregations listed in the select clause. Once groups have been formed.
Retrieve the minimum and maximum salary of clerks for each department having more than three clerks. Apply aggregate functions to each group.
Discard all groups that do not satisfy the condition in the having clause. Note that is not allowed to specify any other column than DEPTNO without an aggregate function in the select clause since this is the only column listed in the group by clause is it also easy to see that other columns would not make any sense.
From these rows form groups according to the group by clause.
The query then would retrieve the minimum and maximum salary of all clerks for each department. Select all rows that satisfy the condition specified in the where clause.
A query containing a group by clause is processed in the following way: Note that a column constraint is a table constraint. Modifying Table. A workaround is to create a temporary table and to copy respective columns and rows into this new table. In this version. Adding Comments to Definitions For applications that include numerous tables. In case that one often refers to tables of other users. This is useful. Table definitions can be modified in an analogous way.
In the most recent version 9i. In earlier versions of Oracle it is not possible to delete single columns from a table definition. If more than only one column should be added at one time. Comments on tables and columns are stored in the data dictionary.. A view can be used in the same way as a table. A view is evaluated again each time it is accessed. The following view contains the name. In Oracle SQL no insert. The optional clause or replace re-creates the view if it already exists.
A with check option can be named using the constraint clause. Production on Sun Dec 20 Release 3. Queries that are frequently issued can be saved to a file and invoked later. Enter user-name: Connected to: Oracle7 Server Release 7. Queries can be parameterized such that it is possible to invoke a saved query with a parameter. All rights reserved.
Instead of this line editor any editor installed on the computer can be invoked. An SQL statement must always be terminated by a semicolon.
Upper and lower case letters are only important for string comparisons. These commands need not be terminated by a semicolon.
In Oracle Version 7 one can get the complete list of possible commands by typing help command. In addition to the SQL statements discussed in the previous section. After exiting the editor the modified SQL statement is stored in the buffer and can be executed command r. You can edit the buffer using the following commands: The command spool off turns spooling off. The relation EMP is automatically created and its structure is derived based on the attributes listed in the select clause.
It is, however, possible to save settings in a file named login. The most frequently used options are: For columns having the data type number, the format command can be used to specify the format before and after the decimal point.
For example, format 99, The command show all displays all variables and their current values. It contains all information about the structures and objects of the database such as tables, columns, users, data files etc. The data stored in the data dictionary are also often called metadata.
Although it is usually the domain of database administrators DBAs , the data dictionary is a valuable source of information for end users and developers. The data dictionary consists of two levels: The external level provides numerous views on these base tables to access information about objects and structures at different levels of detail. An installation of an Oracle database always includes the creation of three standard Oracle users: This is the owner of all data dictionary tables and views.
This user has the highest privileges to manage objects and structures of an Oracle database such as creating new users. This user has less privileges than SYS. All privileges assigned to this user are automatically assigned to all users known in the database.
The selected information includes the name and a short description of each table and view. Each SQL query requires various internal accesses to the tables and views of the data dictionary. Since the data dictionary itself consists of tables, Oracle has to generate numerous SQL statements to check whether the SQL command issued by a user is correct and can be executed.
The external level of the data dictionary provides users a front end to access information relevant to the users. This level provides numerous views in Oracle7 approximately that represent a portion of the data from the base tables in a readable and understandable manner. These views can be used in SQL queries just like normal tables. The views provided by the data dictionary are divided into three groups: The group name builds the prefix for each view name.
For some views, there are associated synonyms as given in brackets below. The structure of these views is analogous to the structure of the USER views. Only users with DBA privileges can access these views.. The DBA views encompass information about all database objects. A cursor basically is a pointer to a query result and is used to read attribute values of selected tuples into variables. Oracle offers several predefined packages. In summary. A cursor typically is used in combination with a loop construct such that each tuple read by the cursor can be processed individually.
In a block. These constructs are necessary in order to implement complex data structures and algorithms. A major restriction of the database language SQL. A package is similar to a module and has an interface and an implementation part.
Blocks allow designers to combine logically related SQL- statements into units. If no header is specified. Blocks that build a procedure. The scope of declared variables i. Valid data types are SQL data types see Section 1.
Each block builds a named program unit. Variables and constants can be declared as follows: If no expression is specified. The not null clause requires that the declared variable must always have a value different from null.
Boolean data may only be true. Thus blocks can be nested like blocks in conventional programming languages. The clause constant states that once a value has been assigned to the variable. Some exceptions are internally defined.
We discuss the usage of cursors in more detail below. Parameters are used to assign values to the variables that are given in the select statement. A cursor declaration specifies a set of tuples as a query result such that the tuples can be processed in a tuple-oriented way i.
We want to retrieve the following attribute values from the table EMP in a tuple- oriented way: Instead of a single variable. Such records are typically used in combination with a cursor. In this case selected tuples are locked and cannot be accessed by other users until a commit has been issued. Instead of specifying a data type. Possible parameter types are char.
We will discuss exception handling in more detail in Section 4.
The cursor name is an undeclared identifier. Latter ones are used in combination with cursors. It is important to ensure that the select statement retrieves at most one tuple! Otherwise it is not possible to assign the attribute values to the specified list of variables and a run- time error occurs. The specification of loops occurs in the same way as known from imperative programming languages such as C or Pascal. The most simple way to assign a value to a variable is declare counter integer: Also in this case.
For most data types. Instead of a list of single variables. All types of loops are used to execute a sequence of statements multiple times. If the select statement retrieves more than one tuple.
The fetch command assigns the selected attribute values of the current tuple to the list of variables. A loop can be named. The associated select statement then is processed and the cursor references the first selected tuple. The example below illustrates how a cursor is used together with a continuous loop: Inside the for loop. Note that the variables in the list must have the same data types as the selected values. Using the keyword reverse causes the iteration to proceed downwards from the higher bound to the lower bound.
The scope of the loop counter is only the for loop. After the fetch command. It overrides the scope of any variable having the same name outside the loop. Processing Cursors: Before a cursor can be used. After all tuples have been processed. Whereas the number of iterations through a while loop is unknown until the loop completes. Cursor for loops can be used to simplify the usage of a cursor: The record sal rec.
That is. For conditional control. If at an iteration no tuple has been fetched.. Each loop can be completed unconditionally using the exit clause: In the example above.
In most cases. The predicate evaluates to true if the most recent fetch failed to return a tuple. A record suitable to store a tuple fetched by the cursor is implicitly declared. A condition can be a simple comparison of values..
We will discuss another version of this block using parameters in Section One can distinguish between two types of exceptions: Note that the record emp rec is implicitly defined. Starting with the first condition. The usage of select statements as in SQL leads to a syntax error.
If update or delete statements are used in combination with a cursor. Except data definition language commands such as create table. The table below lists some of these exceptions with their names and a short description. User defined exceptions. SAL into emp no. After the keyword when a list of exception names connected with or can be specified. System defined exceptions are always automatically raised whenever corresponding errors or warnings occur.
This introduces the default exception handling routine. The last when clause in the exception part may contain the exception name others. After the keyword exception at the end of a block. For this.. A parameter is specified as follows: Valid parameters include all data types. Instead of explicit data types. In order to display numeric variables. The default mode for a parameter is IN.
The percentage of the salary increase is given by a parameter. Here dno is assigned to dept no loop fetch emp cur into empsal. The only difference is that a function returns a value whose data type unconstrained must be specified. IN means that the parameter can be referenced inside the procedure body. If the procedure is called only with the parameter Functions have the same structure as procedures. The optional clauses IN. OUT means that a value can be assigned to the parameter in the body.
IN OUT allows both assigning values to the parameter and referencing the parameter. The above function then can be called using the command execute: A package consists of a package specification and a package body. The package specification defines the interface that is visible for application programmers. Below a package is given that is used to combine all functions and procedures to manage information about employees.
Oracle offers several predefined packages and procedures that can be used by database users and application developers. In order to compile and execute the above package. Below some of the most important procedures of this package are listed: If the program contains errors. If the procedure. Reason for the error Action: Suggested action If this command does not show any errors.
Host variables can be of the following data types: Fortran etc. Host variables are declared according to the C syntax. Embedded SQL provides application programmers a suitable means to combine the computing power of a programming language with the database manipulation and management capabilities of the declarative query language SQL.
Host variables are the key to the communication between the host program and the database. Many data management tasks. The emphasis in this section is placed on the description of the interface.
The resulting C program then can be compiled and linked using a normal C compiler like any other C program. The linker includes the appropriate Oracle specific libraries. Such an interface is provided in the form of Embedded SQL. Declarations of host variables can be placed wherever normal C variable declarations can be placed. Since all these interfaces exhibit comparable functionalities. Fig- ure 1 summarizes the steps from the source code containing SQL statements to an executable program.