Advanced SQL - Database Access from Programming Languages

Accessing Databases From Programming Languages
Database Systems Course
S.Shayan Daneshvar 5.1, 5.2 – 24.4

Why?
a database programmer must have access to a general-purpose programming
language for at least two reasons:
• Not all queries can be expressed in SQL!
• Non-declarative actions; such as printing a report, interacting with a user, or
sending the results of a query to a graphical user interface—cannot be done from
within SQL.

Approaches?
• Dynamic SQL
• Embedded SQL

Standards and API’s for Data Access
• ODBC
• OLE-DB
• JDBC
• ADO/ADO.NET
• LINQ ?
• ODMG Standards (CORBA, …)
• DB-Lib
• HTTP/SOAP
• …

ODBC?
Open Database Connectivity:
The ODBC standard is a widely used standard for communication between client
applications and database systems. ODBC is based on the SQL Call Level Interface
(CLI) standards developed by the X/Open industry consortium and the SQL Access
Group, but it has several extensions.The ODBC API defines a CLI, an SQL syntax
definition, and rules about permissible sequences of CLI calls.
ODBC allows a client to connect simultaneously to multiple data sources and to
switch among them, but transactions on each are independent; ODBC does not
support two-phase commit.
The Open Database Connectivity (ODBC) standard defines an API that applications
can use to open a connection with a database, send queries and updates, and get
back results.

ODBC Example (C/C++)
void ODBCexample()
{
RETCODE error;
HENV env; /* environment */
HDBC conn; /* database connection */
SQLAllocEnv(&env);
SQLAllocConnect(env, &conn);
SQLConnect(conn, "db.kntu.edu", SQL
NTS, "avi", SQL NTS, "avipasswd", SQL
NTS);
{
char deptname[80];
float salary;
int lenOut1, lenOut2;
HSTMT stmt;
char * sqlquery = "select dept name, sum (salary)
from instructor
group by dept name";
SQLAllocStmt(conn, &stmt);
error = SQLExecDirect(stmt, sqlquery, SQL NTS);
if (error == SQL SUCCESS) {
SQLBindCol(stmt, 1, SQL C CHAR, deptname , 80, &lenOut1);
SQLBindCol(stmt, 2, SQL C FLOAT, &salary, 0 , &lenOut2);
while (SQLFetch(stmt) == SQL SUCCESS) {
printf (" %s %gn", depthname, salary);
}
}
SQLFreeStmt(stmt, SQL DROP);
}
SQLDisconnect(conn);
SQLFreeConnect(conn);
SQLFreeEnv(env);
}

ADO and ADO.NET
The Active Data Objects (ADO) API, also created by Microsoft, provides an easy-to-
use interface to the OLE-DB functionality, which can be called from scripting
languages, such asVBScript and JScript.
The newer ADO.NET API is designed for applications written in the .NET languages
such as C# andVisual Basic.NET. In addition to providing simplified interfaces, it
provides an abstraction called the DataSet that permits disconnected data access.
Example: ?

OLE-DB
There are many data sources that are not relational databases, and in fact may not
be databases at all. Examples are flat files and email stores.
Microsoft’s OLE-DB is a C++ API with goals similar to ODBC, but for non-database
data sources that may provide only limited querying and update facilities.
Just like ODBC, OLE-DB provides constructs for connecting to a data source,
starting a session, executing commands, and getting back results in the form of a
rowset, which is a set of result rows. However, OLE-DB differs from ODBC in several
ways ….

JDBC?
Java Database Connectivity:
The JDBC standard defines an application program interface (API) that Java
programs can use to connect to database servers.
The JDBCAPI consists of a set of interfaces and classes written in the Java
programming language.
JDBC is used in languages that use the JVM.
JVM Languages: Java, Kotlin, Scala, Groovy, Clojure, …

JDBC in Details
• Statement
executeQuery()  ResultSet //Query: Select * from Students
executeUpdate()  long // NonQuery: Insert – Delete - Create – Update - …
• Prepared Statement
• Callable Statement

SQL Injection!
Query: "select * from instructor where name = ’" + name + "’“
User Input: X’ or ’Y’ = ’Y
Final Query:
select * from instructor where name = ’X’ or ’Y’ = ’Y’
Solution ?
• Prepared Statement : select * from instructor where name = ’X’ or ’Y’ = ’Y’
• ?

Functions, ProceduresAndTriggers
SQL allows the definition of functions, procedures, and methods.
Note that databases usually have their own notation for stored procedures/functions!
(PL/SQL, T-SQL, PL/pgsql, …)
Standard SQL Example (Function):

Stored Procedures
Standard SQL Example:
Calling Stored Procedures:
PSM (Persistence Storage Module)?

Whole Business logic written in SQL?

Triggers? Methods?
Will talk about them in more details later!
But know that …
Also know that some databases support writing methods in them with a
programming language. IBM DB2 & Oracle support Java Methods.

Back to JDBC
• Callable Statement
CallableStatement cStmt1 = conn.prepareCall("{? = call some function(?)}");
CallableStatement cStmt2 = conn.prepareCall("{call some procedure(?,?)}");
The data types of function return values and out parameters of procedures must be
registered using the method registerOutParameter(), and can be retrieved using get
methods similar to those for result sets. See a JDBC manual for more details.

Other Features
• Metadata Features
• Updatable ResultSet
• Transactional Features (setAutoCommit())
Read About these features in Database Systems Book by Silberschats , …

Embedded SQL
We are not going to talk much about embedded SQL since it is not widely used!
But in Java we have SQLJ!
…

Architectural and Design Patterns
• Repository Architectural Pattern
• DAO
• …
Related Patterns:
• Facade
• …

Mapping? ORM? ODM? ….
• Hibernate, Eclipse Link, OpenJPA, … (Java Persistence API)
• Entity Framework, Nhibernate
• …

Version Control for Database?
• MigrationTools
• Flyway
• Liquibase
• ..

Advanced SQL - Database Access from Programming Languages

Recommended

More Related Content

What's hot (20)

Similar to Advanced SQL - Database Access from Programming Languages (20)

More from S.Shayan Daneshvar (8)

Recently uploaded (20)

Advanced SQL - Database Access from Programming Languages