I'm trying to build a chore app where the user can create a group with a password and they can then add chores to the group that they made. My question is I'm using sqlite as the database and I'm wondering if it's possible to add a database column into the table. I'm planning on creating a table inside my db with columns of id, username, password, database. database is where I will create additional databases where it will store the chore table for my app. If I can't do this, can someone lead me along the way on how I can for example, make a table named Group, then for its columns have id, username, password. Then for each Group rows, be able to somehow match it with another corresponding database or table where the table will be chores with columns say name, frequency. And however many Group rows I add, I will need to somehow make another chore table to match with it, but I need to know how to link and refer to it from just my Group table. If there's a better way to do this using SQLite I would love to know. Thank you.
If i get your question correctly, I think all u need is to use PRIMARY_KEY and FOREIGN_KEY. Hope you are aware of constraints in databases.
So basically two tables will share a KEY which is unique, the key will be the PRIMARY_KEY in table 1 and will act as a link or reference to row in second table, where it is a FOREIGN_KEY
check this for more on constraints
Related
I have some kind of this table.
The question is what is the best way to create this kind of table?
Should I create for each item one table is it possible to create only one table??
Updated: See comments under #Emil.
You should have 1 tables as #Emil has suggested.
This should look like, soemthing like
_id, sort, grade, diameter, length, price1_dol, price1_euros, price2_dol, price2_euros, final,
Note: I have split up prices columns up - so you have price1_dol, price1_euros, price2_dol, price2_euros.
It is indeed possible to make this data into just one table. The columns sort and grade seem to uniquely identify one row so together they might make up a candidate key. If so you could use those as your primary key, or create a new integer column that you use as the primary key.
You should definitely not create one table per item. The database schema should never change with normal use. Only when you add, remove or change the type of data you have in your database should you consider changing the schema. Otherwise you should design and normalize your database in such a way that it's possible to grow the data only by inserting new rows, not new tables.
I am new in programming, and I want to ask question regarding database schema (I'm using SQLite Database for Android Development)
I have some table, let say :
MsMember
MemberId
Password
MsGroup
GroupId
GroupName
MsAnnouncement
AnnouncementId
AnnouncementName
MsComment
CommentId
CommentContent
MsTodolist
TodolistId
TodolistTitle
And I want everytime a new row has been inserted to (at least one of) all five tables above, it will create a notification to user, as far as I know, with this concept, I should create a table to store every detail of notification then shows it to user..
And my best opinion so far is I create a table let say MsNotification, then to connect all five tables with this MsNotification I should have foreign key referring to each table..
My Question is would it be possible (and effective) to have a column that has more than one references?
Example :
Foreign key (SourceId) Referring MsMember (MemberId),
Foreign key(SourceId) referring MsComment (CommentId),
Foreign key (SourceId) referring MsAnnouncement (AnnouncementId), and so on.
or is there any better way to implement this concept?
Thank you in advance
No ,you can not assign single foreign key to multiple column .
But you can put multiple foreign key in single table
I am trying to create one application to store information in sq-lite table.
But i want to take table information from user like table name, columns name, and number of columns, also user can edit that by table name, delete column add new column.
how can i do it.
i add example screen for table filed
Android allows you to execute arbitrary SQL strings. Construct a SQL strings from your UI and then input the string into a command similar to db.execute(string).
Reference
In my Android app, I need to temporarily store some data in a form of table such as follows:
id | column 1 | column 2 | ... | column n
The data are downloaded from a server whenever users press a button. However, the data table doesn't have a fix number of column (as well as row) every time user downloads it from the server. For example, the server may send data with 3 columns the first time. Then it might send data with 5 columns the second time, etc...
Given this scenario, I think the database is probably the right data structure to use. My plan is to create a database, then add and delete tables as necessary. So I have been reading various tutorials on Android database (one example is this one http://www.codeproject.com/Articles/119293/Using-SQLite-Database-with-Android#). It seems to me I cannot create new table with variable number of columns using the sqlite database. Is this correct? In the onCreate(SQLiteDatabase db) method, the "create table" command must be specified with known number of columns and their data types. I could provide several "create table" commands, each with different number of columns but that seems like very crude. Is there a way to create database tables with variable number of columns on the fly?
Another alternative probably using several hash tables, each storing one column of the data table. I'm seriously considering this approach if the database approach is not possible. Any better suggestion is welcomed.
There is no such thing as a variable number of columns in an SQLite data base. Also, adding and deleting tables dynamically seems like a horrible hack.
It sounds like you want to store an array of values associated with an id. I suggest you think in terms of rows, not columns. Use a table structure like (id, index, value); each array of values returned by the server results in as many rows as necessary to store the values.
The Android app that I am currently working on dynamically adds columns to an SQLite database. The problem I have is that I cannot figure out a way to remove these columns from the database.
If I add column A, B, C, D, and E to the database, is it possible to later remove column C?
I have done a lot of looking around and the closest thing I could find was a solution that requires building a backup table and moving all the columns (except the one to be deleted) into that backup table.
I can't figure out how I would do this, though. I add all the columns dynamically so their names are not defined as variables in my Java code. There doesn't seem to be a way to retrieve a column name by using Android's SQLiteDatabase.
SQLite has limited ALTER TABLE support that you can use to add a column to the end of a table or to change the name of a table.
If you want to make more complex changes in the structure of a table, you will have to recreate the table. You can save existing data to a temporary table, drop the old table, create the new table, then copy the data back in from the temporary table.
For example, suppose you have a table named "t1" with columns names "a", "b", and "c" and that you want to delete column "c" from this table. The following steps illustrate how this could be done:
BEGIN TRANSACTION;
CREATE TEMPORARY TABLE t1_backup(a,b);
INSERT INTO t1_backup SELECT a,b FROM t1;
DROP TABLE t1;
CREATE TABLE t1(a,b);
INSERT INTO t1 SELECT a,b FROM t1_backup;
DROP TABLE t1_backup;
COMMIT;
SQLite doesn't support a way to drop a column in its SQL syntax, so its unlikely to show up in a wrapper API. SQLite doesn't often support all features that traditional databases support.
The solutions you've identified make sense and are ways to do it. Ugly, but valid ways to do it.
You can also 'deprecate' the columns and not use them by convention in newer versions of your app. That way older versions of your app that depend on column C won't break.
Oh... just noticed this comment:
The app is (basically) an attendance tracking spreadsheet. You can add
a new "event" and then indicate the people that attended or didn't.
The columns are the "events".
Based on that comment you should just create another table for your events and link to it from your other table(s). You should never have to add columns to support new domain objects like that. Each logical domain object should be represented by its own table. E.g. user, location, event...
Was writing this initially. Will keep it if you're interested:
Instead of dynamically adding and removing columns you should consider using an EAV data model for that part of your database that needs to be dynamic.
EAV data models store values as name/value pairs and the db structure never needs to change.
Based on your comment below about adding a column for each event, I'd strongly suggest creating a second table in which each row will represent an event, and then tracking attendance by storing the user row id and the id of the event row in the attendance table. Continually piling columns onto the attendance table is a definite anti-pattern.
With regards to how to find out about the table schema, you can query the sqlite_master table as described in this other SO question - Is there an SQLite equivalent to MySQL's DESCRIBE [table]?
As per SQLite FAQ, there is only limited support to the ALTER TABLE SQL command. So, the only way you can do is that ou can save existing data to a temporary table, drop the old table, create the new table, then copy the data back in from the temporary table.
Also you can get the column name from the database using a query. Any query say "SELECT * FROM " gives you a cursor object. You can use the method
String getColumnName(int columnIndex);
or
String[] getColumnNames();
to retrieve the names of the columns.