javadb

问题 I have two tables that I join on the id-column, they look like: +-------+ | users | +----+--+---+ | id | name | +----+------+ +-------+ | posts | +-------+------+---------+ | id | user_id | message | +----+---------+---------+ And now I want to select all posts and include the username, with: SELECT * FROM posts, users WHERE user_id = users.id And then I try to get the values with: ResultSet rs = // SQL if(rs.next()) { rs.getInt("posts.id"); ... } But I get SQLException when executing rs

问题 I have two tables that I join on the id-column, they look like: +-------+ | users | +----+--+---+ | id | name | +----+------+ +-------+ | posts | +-------+------+---------+ | id | user_id | message | +----+---------+---------+ And now I want to select all posts and include the username, with: SELECT * FROM posts, users WHERE user_id = users.id And then I try to get the values with: ResultSet rs = // SQL if(rs.next()) { rs.getInt("posts.id"); ... } But I get SQLException when executing rs

问题 Consider the following table: create table language ( id integer generated always as identity (START WITH 1, INCREMENT BY 1), name long varchar, constraint language_pk primary key (id) ); To which I'd insert an entry this way. insert into language(name) values ('value'); How does one know what value for id was created? Just doing a SELECT using the name field is not valid, because there can be duplicate entries. 回答1: Through plain SQL: insert into language(name) values ('value'); SELECT

问题 How can I truncate a VARCHAR to the table field length AUTOMATICALLY in Derby using SQL? To be specific: CREATE TABLE A ( B VARCHAR(2) ); INSERT INTO A B VALUES ('1234'); would throw a SQLException: A truncation error was encountered trying to shrink VARCHAR '123' to length 2. Is there a easy way to suppress this exception? 回答1: No. You should chop it off after checking the meta-data. Or if you don't wanna check the meta-data everytime, then you must keep both your code and database in sync.

问题 How can I truncate a VARCHAR to the table field length AUTOMATICALLY in Derby using SQL? To be specific: CREATE TABLE A ( B VARCHAR(2) ); INSERT INTO A B VALUES ('1234'); would throw a SQLException: A truncation error was encountered trying to shrink VARCHAR '123' to length 2. Is there a easy way to suppress this exception? 回答1: No. You should chop it off after checking the meta-data. Or if you don't wanna check the meta-data everytime, then you must keep both your code and database in sync.

问题 I am using JavaDB for the first time and I am having trouble getting my program to run. Whenever I run it I get this error: "Error connecting to server localhost on port 1527 with message Connection refused: connect" My database and code are all setup okay as when I ran it on someone elses computer it worked fine, but on mine it doesn't. I'm using Netbeans 7.3.1 as that is the version I have to use for school. I am not sure what is causing this and I could really use some help. If you have

问题 First, this is my first time with Apache Derby. I am using netbeans, willing to use embedded apache derby, and I followed the following tutorial for configuring and installing the database http://netbeans.org/kb/docs/ide/java-db.html#starting The attached image will show my database status in netbeans My database name is "contact". Table name is "FRIENDS". Following is my test code DatabaseConnector.java import java.sql.*; public class DataBaseConnector { private Connection con; public

问题 First, this is my first time with Apache Derby. I am using netbeans, willing to use embedded apache derby, and I followed the following tutorial for configuring and installing the database http://netbeans.org/kb/docs/ide/java-db.html#starting The attached image will show my database status in netbeans My database name is "contact". Table name is "FRIENDS". Following is my test code DatabaseConnector.java import java.sql.*; public class DataBaseConnector { private Connection con; public

问题 I am midway through a database application(SWING). I am using Java DB and NetBeans 7.1.2. Within the IDE, the app runs good, provided I initially connect the database manually in the 'services' window. Also, I have added the derby.jar and derbyclient.jar files to the libraries. But when running the app from the "dist" folder, it fails to connect to the database. I want to know whether i can attach the db within the jar file so that i can run the app from outside the IDE. Thank you. 回答1: You

问题 Is it possible to create table and it's name in lower case using JavaDB/Derby? To check if table exists I'm using: ResultSet rs = dbmd.getTables(null, "APP", "user_properties", null); if (!rs.next()) {/*do something*/}; But table name 'user_properties' must mach the case in catalog. 回答1: Derby follows the ANSI standard which requires unquoted identifiers to be folded to uppercase. So, the following statement: create table user_properties ( id integer not null ); will create a table with then