JAVA JDBC WITH SPRING DETAILS AND BASICS

1. SQL and JDBC
Peter Mork

2. Database Primer*
 All data values are simple
 No arrays, pointers, vectors, complex types
 All data are stored as 2D tables/relations
 Contains 0 or more rows/tuples
 Contains 1 or more columns/attributes
 All operations defined logically
 Order of tuples is irrelevant
 Keys used to identify unique tuples
* SQL Instant Reference by Martin Gruber

3. SQL: What is it?
 Data Definition Language (DDL)
 CREATE relations, attributes, etc.
 Data Manipulation Language (DML)
 INSERT, UPDATE or DELETE data
 Data Control Language (DCL)
 GRANT, REVOKE privileges
 Data Query Language (DQL)
 SELECT data from relations

4. CREATE-ing Relations
CREATE TABLE {name}
( {col1} {type1} [{cons1}],
{col2} {type2} [{cons2}],
...
);
col? = A name for the column
type? = The column’s data-type
cons? = An optional constraint on the column

5. Data types
 CHAR(len), VARCHAR(len): Strings of
maximum length len
 FLOAT, REAL: Approximate numbers
 INT, INTEGER: Exact integers
 DECIMAL, DEC: Exact decimals
 DATE, TIME, TIMESTAMP: Timestamp
combines date and time

6. Constraints
 NOT NULL: No missing data allowed
 UNIQUE: Every value is unique or
missing
 PRIMARY KEY: Every value is unique
 Plus other more sophisticated
predicates

7. Example
CREATE TABLE students
( s_id INT PRIMARY KEY,
s_name VARCHAR(50) NOT NULL,
s_dob DATE
);
s_id s_name s_dob

8. INSERT-ing New Values
INSERT INTO {table}
[ ( {col-a}, {col-b}, … ) ]
VALUES ( {val-a}, {val-b}, … );
col-x = Optional column names
val-x = A value for that column
If no column names are given, the order
in the CREATE statement is used.

9. Example
INSERT INTO students
VALUES ( 001, ‘Peter Mork’ );
 Since no column names were specified:
 001 is s_id
 ‘Peter Mork’ is s_name
 NULL is used for missing data
s_id s_name s_dob
1 Peter Mork NULL

10. DELETE-ing Values
DELETE FROM {table}
[ WHERE {predicate} ];
 Deletes all tuples from {table} that
match {predicate}
 Use a primary key to isolate one tuple
Example:
DELETE FROM students
WHERE s_id = 1;

11. SELECT-ing Results
SELECT {attr-list}
FROM {table-list}
[ WHERE {pred-list} ];
Logically:
 Computes cross-product of all tables
 Discards results that don’t match predicates
 Returns listed attributes

12. Simple Example
SELECT s_name
FROM students
WHERE s_dob > ‘1975-1-1’;
This retrieves all students born since
1975.

13. SELECT Clause
 An attribute list is either:
 * (indicating all columns)
 A list of unique attribute names:
 Usually an attribute name will suffice
 Sometimes you need {table}.{attr}
 Can rename attributes using AS
Example:
SELECT students.s_id AS id,
s_name, grades.grade

14. FROM Clause
 A table list is a list of unique table
names:
 Usually a table name will suffice
 Multiple occurrences of the same table
must be renamed using AS
Example:
FROM students, final_grades AS
grades

15. WHERE Clause
 The predicate list contains
 Join predicates, which relate two columns
from different tables
 Select predicates, which relate a column to a
constant or another column in the same
table
Example:
WHERE grade >= 3.0
AND students.s_id = grades.s_id;

16. Full Example
SELECT students.s_id AS id,
s_name, grades.grade
FROM students,
final_grades as grades
WHERE grade >= 3.0
AND students.s_id =
grades.s_id;

17. Sample Data
s_id s_name s_dob
1 Alice NULL
2 Bob 1974-8-28
3 Cindy 1973-10-19
s_id course grade
1 544 3.5
1 521 3.8
1 531 3.9
2 544 3.6
2 551 2.9

18. Cross-Product Results
students.s_id s_name s_dob grades.s_id course grade
1 Alice NULL 1 544 3.5
1 Alice NULL 1 521 3.8
1 Alice NULL 1 531 3.9
1 Alice NULL 2 544 3.6
1 Alice NULL 2 551 2.9
2 Bob 1974-8-28 1 544 3.5
2 Bob 1974-8-28 1 521 3.8
2 Bob 1974-8-28 1 531 3.9
2 Bob 1974-8-28 2 544 3.6
2 Bob 1974-8-28 2 551 2.9
3 Cindy 1973-10-19 1 544 3.5
3 Cindy 1973-10-19 1 521 3.8
3 Cindy 1973-10-19 1 531 3.9
3 Cindy 1973-10-19 2 544 3.6
3 Cindy 1973-10-19 2 551 2.9

19. Check Predicates
students.s_id s_name s_dob grades.s_id course grade
1 Alice NULL 1 544 3.5
1 Alice NULL 1 521 3.8
1 Alice NULL 1 531 3.9
1 Alice NULL 2 544 3.6
1 Alice NULL 2 551 2.9
2 Bob 1974-8-28 1 544 3.5
2 Bob 1974-8-28 1 521 3.8
2 Bob 1974-8-28 1 531 3.9
2 Bob 1974-8-28 2 544 3.6
2 Bob 1974-8-28 2 551 2.9
3 Cindy 1973-10-19 1 544 3.5
3 Cindy 1973-10-19 1 521 3.8
3 Cindy 1973-10-19 1 531 3.9
3 Cindy 1973-10-19 2 544 3.6
3 Cindy 1973-10-19 2 551 2.9

20. Final Result
id s_name Grade
1 Alice 3.5
1 Alice 3.8
1 Alice 3.9
2 Bob 3.6

21. Note
This is the logical order of operations. The
database system will not choose such a
brain-damaged approach.
Application developers/users do not need
to know how to execute the query
efficiently; access plans are chosen
automatically by the database system.

22. Other capabilities
 Grouping and aggregation
 Uses GROUP BY keyword
 Aggregation functions include:
 COUNT
 SUM
 AVG
 More sophisticated predicates
 Nested queries

23. JDBC: What is it?
 API for database programs
 Collection of interfaces, and a few key
classes
 Relies on vendor-supplied drivers (i.e.,
implementations of the interfaces)

24. Connectivity Protocols
JDBC
 Driver registered
with system
 Downloaded (linked
at run-time by VM)
 Written in Java
 can be linked to an
existing ODBC driver
ODBC
 Driver registered
with system
 Installed on host
machine
 Written in C
 de facto standard

25. JDBC Classes
 Date, Time, Timestamp, Types
 Represent standard RDB types
 Mapped to Java type system
 DriverManager/DriverPropertyInfo
 Used to initialize driver
 Analogous to the System class

26. JDBC Interfaces
 Driver/Connection
 Used to communicate with database
 Statement (Callable, Prepared)
 Used to package SQL
 ResultSet
 Used to iterate through query result (cursor)
 DatabaseMetadata/ResultSetMetaData
 Contains data about the data

27. Steps to manipulate DB
1. Load driver
2. Connect to database
3. Manipulate data
4. Close database

28. 1. Load driver
 Explicitly:
Class.forName(“driver name”)
This creates a new instance of the driver
 Implicitly:
Update the Java system settings
(See Java docs for more info)

29. 2. Connect to database
 getConnection(db)
 getConnection(db, uid, pwd)
 getConnection(db, info)
db = “jdbc:odbc:data-source-name”
db = “jdbc:???://host:port/dbname”

30. Connection notes
 Properties is a sub-class of HashTable
 Used to package multiple parameters
 close() closes a connection (step 4)
 isClosed() tests a connection’s status

31. 3. Manipulate data
 createStatement establishes a
framework for executing queries
 executeQuery returns a ResultSet
 executeUpdate returns an int
 execute can return either, but is usually
used when there is no data to return

32. Which execute to execute?
 DDL and DCL queries are generally run
using execute()
 DML queries are generally run using
executeUpdate(); the return value
represents the number of rows affected
 DQL queries are generally run using
executeQuery(); a collection of tuples is
returned

33. ResultSet
 A cursor that iterates through a
collection of tuples
 Forward only!
 Each Statement object can have at most
one active ResultSet

34. Metadata
 Metadata lets you know what the
database looks like
 Information about the table names,
field names, domains, etc.
 Metadata exists for both the Database
(effectively constant) and for each
ResultSet (depends on the query)

35. Important Metadata methods
 columnCount(): The number of fields in
a ResultSet
 columnType(i): The type (as listed in
Types) of column i. Note that columns
are 1-indexed, not 0.
 The return value of columnType can be
used to select the correct getXXX
method to invoke on the ResultSet

36. Possible Uses of JDBC
 Leverage Java’s GUI tools to allow users
to visualize the contents of a database
 Use Java to publish information stored
in a database on the web
 Create tools to aid the database
programmer in designing queries

37. Observations
 Java’s inherent speed problems can be
offset by the power of an efficient
database
 Many databases have awkward user
interfaces
 Database queries are disk/network
requests -- think multi-threading