Unit2_Advanced_SQl

Chapter 4: Advanced SQL: 

Chapter 4: Advanced SQL

Chapter 4: Advanced SQL: 

SQL Data Types and Schemas Integrity Constraints Authorization Embedded SQL Dynamic SQL Functions and Procedural Constructs** Recursive Queries** Advanced SQL Features** Chapter 4: Advanced SQL

Built-in Data Types in SQL : 

date: Dates, containing a (4 digit) year, month and date Example: date ‘2005-7-27’ time: Time of day, in hours, minutes and seconds. Example: time ‘09:00:30’ time ‘09:00:30.75’ timestamp : date plus time of day Example: timestamp ‘2005-7-27 09:00:30.75’ interval: period of time Example: interval ‘1’ day Subtracting a date/time/timestamp value from another gives an interval value Interval values can be added to date/time/timestamp values Built-in Data Types in SQL

User-Defined Types: 

create type construct in SQL creates user-defined type create type Dollars as numeric (12,2) final create domain construct in SQL-92 creates user-defined domain types create domain person_name char (20) not null Types and domains are similar. Domains can have constraints, such as not null , specified on them. User-Defined Types

Domain Constraints: 

Domain constraints are the most elementary form of integrity constraint. They test values inserted in the database, and test queries to ensure that the comparisons make sense. New domains can be created from existing data types Example: create domain Dollars numeric (12, 2) create domain Pounds numeric (12,2) Domain Constraints

Large-Object Types: 

Large objects (photos, videos, CAD files, etc.) are stored as a large object : blob : binary large object -- object is a large collection of uninterpreted binary data (whose interpretation is left to an application outside of the database system) clob : character large object -- object is a large collection of character data When a query returns a large object, a pointer is returned rather than the large object itself. Large-Object Types

Integrity Constraints: 

Integrity constraints guard against accidental damage to the database, by ensuring that authorized changes to the database do not result in a loss of data consistency. A customer must have a (non-null) phone number Integrity Constraints

Constraints on a Single Relation : 

not null primary key check ( P ) , where P is a predicate Constraints on a Single Relation

Not Null Constraint : 

Declare branch_name for branch is not null branch_name char (15) not null Declare the domain Dollars to be not null create domain Dollars numeric (12,2) not null Not Null Constraint

The check clause: 

check ( P ) , where P is a predicate The check clause Example: Declare branch_name as the primary key for branch and ensure that the values of assets are non-negative. create table branch ( branch_name char (15) , branch_city char (30), assets integer , primary key ( branch_name ) , check ( assets >= 0))

The check clause (Cont.): 

The check clause in SQL-92 permits domains to be restricted: Use check clause to ensure that an hourly_wage domain allows only values greater than a specified value. create domain hourly_wage numeric(5,2) constraint value_test check ( value > = 4.00) The domain has a constraint that ensures that the hourly_wage is greater than 4.00 The clause constraint value_test is optional; useful to indicate which constraint an update violated. The check clause (Cont.)

Referential Integrity: 

Ensures that a value that appears in one relation for a given set of attributes also appears for a certain set of attributes in another relation. Example: If “Perryridge” is a branch name appearing in one of the tuples in the account relation, then there exists a tuple in the branch relation for branch “Perryridge”. Primary and candidate keys and foreign keys can be specified as part of the SQL create table statement: The primary key clause lists attributes that comprise the primary key. The foreign key clause lists the attributes that comprise the foreign key and the name of the relation referenced by the foreign key. By default, a foreign key references the primary key attributes of the referenced table. Referential Integrity

Referential Integrity in SQL – Example: 

create table customer ( customer_name char (20) , customer_street char (30), customer_city char (30), primary key ( customer_name )) create table branch (branch_name char (15) , branch_city char (30), assets numeric (12,2), primary key ( branch_name )) Referential Integrity in SQL – Example

Referential Integrity in SQL – Example (Cont.): 

create table account ( account_number char (10) , branch_name char (15), balance integer , primary key ( account_number), foreign key ( branch_name ) references branch ); create table depositor ( customer_name char (20) , account_number char (10) , primary key ( customer_name, account_number), foreign key ( account_number ) references account, foreign key ( customer_name ) references customer ); Referential Integrity in SQL – Example (Cont.)

Slide 15: 

Large object Book_review clob(15KB) Image blob(10MB) Movie blob(2GB)

Assertions: 

An assertion is a predicate expressing a condition that we wish the database always to satisfy. An assertion in SQL takes the form create assertion <assertion-name> check <predicate> When an assertion is made, the system tests it for validity, and tests it again on every update that may violate the assertion This testing may introduce a significant amount of overhead; hence assertions should be used with great care. Assertions

Assertion Example: 

The sum of all loan amounts for each branch must be less than the sum of all account balances at the branch. create assertion sum_constraint check ( not exists ( select * from branch where ( select sum ( amount ) from loan where loan.branch_name = branch.branch_name ) >= ( select sum ( amount ) from account where loan.branch_name = branch.branch_name ))) Assertion Example

Authorization: 

Authorization Forms of authorization on parts of the database: Read - allows reading, but not modification of data. Insert - allows insertion of new data, but not modification of existing data. Update - allows modification, but not deletion of data. Delete - allows deletion of data. Forms of authorization to modify the database schema Index - allows creation and deletion of indices. Resources - allows creation of new relations. Alteration - allows addition or deletion of attributes in a relation. Drop - allows deletion of relations.

Authorization Specification in SQL: 

Authorization Specification in SQL The grant statement is used to confer authorization grant <privilege list> on <relation name or view name> to <user list> <user list> is: a user-id public , which allows all valid users the privilege granted Granting a privilege on a view does not imply granting any privileges on the underlying relations. The grantor of the privilege must already hold the privilege on the specified item (or be the database administrator).

Privileges in SQL: 

Privileges in SQL select : allows read access to relation, or the ability to query using the view Example: grant users U 1 , U 2 , and U 3 select authorization on the branch relation: grant select on branch to U 1 , U 2 , U 3 insert : the ability to insert tuples update : the ability to update using the SQL update statement delete : the ability to delete tuples. all privileges : used as a short form for all the allowable privileges

Revoking Authorization in SQL: 

Revoking Authorization in SQL The revoke statement is used to revoke authorization. revoke <privilege list> on <relation name or view name> from <user list> Example: revoke select on branch from U 1 , U 2 , U 3 <privilege-list> may be all to revoke all privileges the revokee may hold. If <revokee-list> includes public, all users lose the privilege except those granted it explicitly. If the same privilege was granted twice to the same user by different grantees, the user may retain the privilege after the revocation. All privileges that depend on the privilege being revoked are also revoked.

Embedded SQL: 

The SQL standard defines embeddings of SQL in a variety of programming languages such as C, Java, and Cobol. A language to which SQL queries are embedded is referred to as a host language , and the SQL structures permitted in the host language comprise embedded SQL. EXEC SQL statement is used to identify embedded SQL request to the preprocessor EXEC SQL <embedded SQL statement > END_EXEC Note: this varies by language (for example, the Java embedding uses # SQL { …. }; ) Embedded SQL

Example Query: 

Specify the query in SQL and declare a cursor for it EXEC SQL declare c cursor for select depositor.customer_name, customer_city from depositor, customer, account where depositor.customer_name = customer.customer_name and depositor account_number = account.account_number and account.balance > :amount END_EXEC Example Query From within a host language, find the names and cities of customers with more than the variable amount dollars in some account. Cursor- It is a temporary table which retrieve number of rows as per request & keep it in main memory.

Embedded SQL (Cont.): 

The open statement causes the query to be evaluated EXEC SQL open c END_EXEC The fetch statement causes the values of one tuple in the query result to be placed on host language variables. EXEC SQL fetch c into : cn, :cc END_EXEC Repeated calls to fetch get successive tuples in the query result The close statement causes the database system to delete the temporary relation that holds the result of the query. EXEC SQL close c END_EXEC Embedded SQL (Cont.)

Updates Through Cursors: 

Updates Through Cursors Can update tuples fetched by cursor by declaring that the cursor is for update declare c cursor for select * from account where branch_name = ‘Perryridge’ for update To update tuple at the current location of cursor c update account set balance = balance + 100 where current of c

Dynamic SQL: 

Allows programs to construct and submit SQL queries at run time. Example of the use of dynamic SQL from within a C program. char * sqlprog = “ update account set balance = balance * 1.05 where account_number = ?” EXEC SQL prepare dynprog from :sqlprog; char account [10] = “A-101”; EXEC SQL execute dynprog using :account; The dynamic SQL program contains a ?, which is a place holder for a value that is provided when the SQL program is executed. Dynamic SQL

ODBC and JDBC: 

API (application-program interface) for a program to interact with a database server Application makes calls to Connect with the database server Send SQL commands to the database server Fetch tuples of result one-by-one into program variables ODBC (Open Database Connectivity) works with C, C++, C#, and Visual Basic JDBC (Java Database Connectivity) works with Java ODBC and JDBC

ODBC: 

ODBC Open DataBase Connectivity(ODBC) standard standard for application program to communicate with a database server. application program interface (API) to open a connection with a database, send queries and updates, get back results. Applications such as GUI, spreadsheets, etc. can use ODBC

ODBC (Cont.): 

ODBC (Cont.) Each database system supporting ODBC provides a "driver" library that must be linked with the client program. When client program makes an ODBC API call, the code in the library communicates with the server to carry out the requested action, and fetch results.

JDBC: 

JDBC is a Java API for communicating with database systems supporting SQL JDBC supports a variety of features for querying and updating data, and for retrieving query results JDBC also supports metadata retrieval, such as querying about relations present in the database and the names and types of relation attributes Model for communicating with the database: Open a connection Create a “statement” object Execute queries using the Statement object to send queries and fetch results Exception mechanism to handle errors JDBC

Procedural Extensions and Stored Procedures: 

Procedural Extensions and Stored Procedures SQL provides a module language Permits definition of procedures in SQL, with if-then-else statements, for and while loops, etc. Stored Procedures Can store procedures in the database then execute them using the call statement permit external applications to operate on the database without knowing about internal details.

Functions and Procedures: 

SQL:1999 supports functions and procedures Functions/procedures can be written in SQL itself, or in an external programming language Functions are particularly useful with specialized data types such as images and geometric objects Some database systems support table-valued functions , which can return a relation as a result SQL:1999 also supports a rich set of imperative constructs, including Loops, if-then-else, assignment Functions and Procedures

Procedure: 

create procedure account_count_proc (in title varchar (20), out a_count integer) begin select count( author) into a_count from depositor where depositor.customer_name = account_count_proc.customer_name End; //in parameter is a call by value parameter //out parameter is call by reference parameter Procedure

Slide 34: 

Procedure salinc(ecd in number(5)) is msal emp.salary %type; Begin Select sal into msal from emp where ecode=ecd; if(msal>=5000) then msal=msal+msal*0.15; Else msal=msal+msal*0.10; Endif Update emp set sal=msal where ecode=ecd; End;//sql>execute salinc(101);

Function: 

Function SQL Functions 􀂄Define a function that, given the name of a customer, returns the count of the number of accounts owned by the customer. create function account_count (customer_name varchar(20)) returns integer begin declare a_count integer; select count ( * ) into a_count from depositor where depositor.customer_name = customer_name; return a_count; end

External Language Routines: 

External Language Routines Benefits of external language functions/procedures: more efficient for many operations, and more expressive power Drawbacks Code to implement function may need to be loaded into database system and executed in the database system’s address space risk of accidental corruption of database structures security risk, allowing users access to unauthorized data There are alternatives, which give good security at the cost of potentially worse performance Direct execution in the database system’s space is used when efficiency is more important than security

Recursion in SQL: 

SQL:1999 permits recursive view definition Example: find all employee-manager pairs, where the employee reports to the manager directly or indirectly (that is manager’s manager, manager’s manager’s manager, etc.) with recursive empl ( employee_name , manager_name ) as ( select employee_name, manager_name from manager union select manager. employee_name , empl . manager_name from manager , empl where manager . manager_name = empl . emp loye_name) select * from empl This example view, empl, is called the transitive closure of the manager relation Recursion in SQL