Be sure that derby.jar is either:

If you are using JDK 1.5 or greater, a LinkageError will occur. Removing the mx4j-3.0.2.jar library from %GROOVY_HOME%\lib will make it work again, but a better solution would be preferable.
Look at http://jira.codehaus.org/browse/GROOVY-2303 for further information, or ask on the user@groovy.codehaus.org.

This will create derby.log and derbyDB folder in the folder where the script is.

If something goes wrong, simply remove derbyDB folder, and everything will be clean for next run. 

//uncomment the next line to load the derby jar at runtime :
//set CLASSPATH=%CLASSPATH%;d:\\path\\to\\derby.jar

import groovy.sql.*
import java.sql.*

protocol = 'jdbc:derby:'
def props = new Properties()
props.put('user', 'user1')
props.put('password', 'user1')

def sql = Sql.newInstance("${protocol}derbyDB;create=true", props)

/* Creating table, adding few lines, updating one */
sql.execute('create table people(id int, name varchar(40), second_name varchar(40), phone varchar(30), email varchar(50))')

println("Created table 'people'")

sql.execute("insert into people values (1,'John', 'Doe', '123456','johndoe@company.com')")
sql.execute("insert into people values (2,'Bill', 'Brown', '324235','billbrown@company.com')")
sql.execute("insert into people values (3,'Jack', 'Daniels', '443323','jackdaniels@company.com')")

println('Inserted people')

sql.execute("update people set phone='443322', second_name='Daniel''s'where id=3")

println('Updated person')

/* Simple query */
def rows = sql.rows('SELECT * FROM people ORDER BY id')
rows.each {println it}

/* Dropping table 'people' */
sql.execute('drop table people')
println ("Table 'people' dropped")

try{
DriverManager.getConnection('jdbc:derby:;shutdown=true')
}
catch (SQLException se){
   gotSQLExc = true
}

println('Finish!')