C20.0046: Database
Management Systems
Lecture #18
Matthew P. Johnson
Stern School of Business, NYU
Spring, 2004
M.P. Johnson, DBMS, Stern/NYU, Sp2004
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Agenda
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Previously: Pro*C
Next:
Project part 3 is due next week
More programming for SQL
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Embedded SQL
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Pro*C, SQLJ
PSMs
CLI
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SQL/CLI in C
JDBC in Java
DBI/DBDs in Perl
PHP (HTML?)
M.P. Johnson, DBMS, Stern/NYU, Sp2004
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Recap: Embedded SQL
prog.pc
Host language + Embedded SQL
Preprocessor
Preprocessor
prog.c
Host Language + function calls
Host
Host language
language compiler
compiler
a.out
Oracle’s
Pro*C
gcc
Executable
M.P. Johnson, DBMS, Stern/NYU, Sp2004
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Limitation of embedded SQL
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Okay for apps with a fixed set of
queries/updates
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But consider, say, sqlplus or the sqlzoo
website
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Maybe very simple kiosks
Processes arbitrary queries from user
Can we do this with embedded SQL?
M.P. Johnson, DBMS, Stern/NYU, Sp2004
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Dynamic SQL
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In dynamic SQL, query string can be taken as a
parameter, passed to DB
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Two steps:
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Combine together: EXECUTE IMMEDIATE
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Prepare: compiles/optimizes the string
Execute: executes the query
But separate if query is executed many times (why?)
Something like the sqlplus program could be written
as a simple dynamic SQL
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future homework idea?
M.P. Johnson, DBMS, Stern/NYU, Sp2004
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Dynamic SQL
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myquery = a SQL variable
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not prefixed by :
void someQuery() {
EXEC SQL BEGIN DECLARE SECTION;
char *command;
EXEC SQL END DECLARE SECTION;
/* command set to some query string */
EXEC SQL PREPARE myquery FROM :command;
EXEC SQL EXECUTE myquery;
/* or just: */
EXEC SQL EXECUTE IMMEDIATE myquery;
}
M.P. Johnson, DBMS, Stern/NYU, Sp2004
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Dynamic SQL example
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Example script: sample8.pc
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See Pro*C tutorial
Goal: find employees from department 10
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Start with query as string
sales% proc sample8.pc
sales% gcc -I/oracle/precomp/public
/oracle/lib/libclntsh.so
–osample8 sample8.c
sales% sample8
M.P. Johnson, DBMS, Stern/NYU, Sp2004
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Sketch of sqlplus/mysql
EXEC SQL BEGIN DECLARE SECTION;
char query[MAX QUERY LENGTH];
EXEC SQL END DECLARE SECTION;
/* issue SQL> prompt */
/* read user's text into array query */
EXEC SQL EXECUTE IMMEDIATE :query;
/* go back to reissue prompt */
M.P. Johnson, DBMS, Stern/NYU, Sp2004
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Dynamic SQL example 2
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Example script: sample10.pc
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See Pro*C tutorial
Goal: recreate sqlplus/mysql
sales% proc sample10.pc
sales% gcc -I/oracle/precomp/public
/oracle/lib/libclntsh.so
–osample10 sample10.c
sales% sample10
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Copy-able commands:
http://pages.stern.nyu.edu/~mjohnson/dbms/eg/lec18/proc.txt
M.P. Johnson, DBMS, Stern/NYU, Sp2004
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Next topic: SQL/CLI
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Pro*C converts EXEC SQL code
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--into what?
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If we know the API (“Call-Level Interface”),
can call library routines by hand
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Is this better or worse?
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Pros & cons
Won’t cover in depth
M.P. Johnson, DBMS, Stern/NYU, Sp2004
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CLI: Java
prog.pc
Host language + Embedded SQL
Preprocessor
Preprocessor
Prog.java
Host Language + function calls
Host
Host language
language compiler
compiler
Proj.class
Oracle’s
Pro*C
javac + jar
Executable
M.P. Johnson, DBMS, Stern/NYU, Sp2004
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CLI - Overview
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Similar to what really happens in embedded SQL
implementations.
Major approaches:
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Advantages over embedded SQL:
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SQL/CLI - standard of ODBC
JDBC (Java database connectivity)
See http://cbbrowne.com/info/middleware.html for many
options
Avoid preprocessor-stage, easier to debug
In th., use same program with several DBMS
Disadvantages:
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Must keep up to date with API changes
DBMS may have conflicting APIs
M.P. Johnson, DBMS, Stern/NYU, Sp2004
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Next topic: JDBC (Java’s CLI)
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As expected: Java too can talk to SQL
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In some ways: much nicer
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JDBC is an interface
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Changes very little
Each vendor writes own plug-in
Dev. Strategy: write to API, compile with jar
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See http://servlet.java.sun.com/products/jdbc/drivers
for 202 (!) JDBC drivers
M.P. Johnson, DBMS, Stern/NYU, Sp2004
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JDBC
1.
Load JDBC driver for DBMS:
Class.forName("oracle.jdbc.driver.OracleDriver")
2.
Obtain a connection:
Connection con = DriverManager.getConnection(
“jdbc:oracle:thin:@l5.nyu.edu:1521:STN1",
username, passwd);
M.P. Johnson, DBMS, Stern/NYU, Sp2004
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JDBC
3.
Obtain a statement object:
Statement stmt = con.createStatement();
4.
Run a query:
stmt.executeQuery(“SELECT * FROM table”);
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Or an update:
stmt.executeUpdate(“INSERT INTO tables” +
“VALUES(‘abc’, ‘def’)”);
M.P. Johnson, DBMS, Stern/NYU, Sp2004
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Prepared Statements in JDBC
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JDBC also supports prepared statements
3.
Obtain a PreparedStatement object:
PreparedStatement ps = con.createStatement(
“SELECT * FROM table”);
4.
Now execute:
ps.executeQuery();
M.P. Johnson, DBMS, Stern/NYU, Sp2004
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Obtaining query results
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“Cursor” not used, but same idea
executeQuery() return a ResultSet:
ResultSet rs = ps.executeQuery();
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rs.next() advances to new row, returns false if EOF
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getInt(i) returns ith column (if an int!) from current row
while (rs.next()) {
String val1 = rs.getString(1);
int val2 = rs.getInt(2);
…
}
M.P. Johnson, DBMS, Stern/NYU, Sp2004
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Java/JDBC/Oracle example
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Example program: SQLRunner.java
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Goal: run the SQL query passed
sales% cp ~mjohnson/public_html/dbms/eg/lec17/*.java
sales% javac SQLRunner.java
sales% java SQLRunner
"select table_name from user_tables"
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Copy-able commands:
http://pages.stern.nyu.edu/~mjohnson/dbms/eg/lec1
8/jdbc.txt
M.P. Johnson, DBMS, Stern/NYU, Sp2004
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Java/JDBC/MySQL example
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Example program: MySQLRunner.java
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Goal: run the SQL query passed
sales% cp ~mjohnson/public_html/dbms/eg/lec17/*.jar
sales% javac MySQLRunner.java
sales% java -cp .:mysql.jar
MySQLRunner "select * from mytab"
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(Nearly) the same as before!
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just using different DB/tables/login
mysql.jar is the MySQL J/Connector jar
M.P. Johnson, DBMS, Stern/NYU, Sp2004
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