I am develop app that Store to a table some Todo tasks with a - Topics and sub-topics. I thought of two ways to do this action, but what is the best way recommended. Way number 1 : is to add to my table - column with the sub-topics names, and when i want to show this specific Topic just do a for loop query for him.
way number 2 : is create 2 tables that handle the topics is and names and the other one handle the sub-topics data.
If you are only going to have one tag on each row, then the first method is fine.
If you are going to allow multiple tags on a row, then use a junction table, which is the todo_tags table in the second approach. The junction table is the right method for storing lists of objects (tags) attached to another list.
Related
I put my data in 3 tables(Links, Images and PDF)
each table has columns(university, faculty, grade, and description,...)
I want to retrieve description column in the 3 tables.
where university, faculty, and grade equal to certain values.
and sort them with creation date.
how can I perform that query in parse?
I'm not familiar with Android, but I'm pretty sure Parse does not support "Join" in the way a SQL database does. You could nest the queries, performing the next one in the previous one's completion block.
However, if you regularly want to get data from those 3 tables, I'd suggest you make it 1 table instead, with a column "Content" instead of Link/Img/PDF. Images and PDFs would probably be stored as PFFiles anyway, and you can put link as either its own string column or putting it in a file. You could also add a column "type" if you want to be able to query a specific type, or just keep track of which columns contains which data.
Then you could query the "Content" class, on the keys you want.
I think this link might help you
https://parse.com/docs/js/guide#relations and it is quite simple and nicely explained . You can't do it directly in the database, though.
I have in my db 2 table with a many to many relationship.
TAB_ARTICLES: {_ID, TITLE, BODY, DATE}
TAB_TAG: {_ID, NAME, COLOR, DATE}
TAB_ART_TAG: {_ID, ARTICLE_ID, TAG_ID}
I need to populate a ListView, one row for article and in every row I need to have a TextView for every label linked to that article. Like the following image
I think 2 solutions.
a. I use a CursorAdapter with a cursor made only on TAB_ARTICLE and than in every row I do a query to join the other 2 tables looking for all tags related at this article. This solution require a lot of db accesses.
b. I realize a temporary table
TABLE_TEMP: {ARTICLE_TITLE, ARTICLE_BODY, ARTICLE_DATE, TAG1_NAME, TAG1_COLOR, TAG2_NAME, TAG2_COLOR, ...}
and I use a query on this table as cursor for custom adapter. This solution use more space and have a limitation on possible displayed tags due to table columns.
Are there other ways?
Well, actually, it's a multicriterion thing: time, space, updates, search, etc. So there's no single recipe. It's very probable, however, that multiple queries will bog down scrolling. Worse, on some devices only. A temporary table may or may not be OK depending on the overall size of your data. And you may want to keep this redundant table in sync with the main one, making simultaneous updates to both.
One of the simplest trade-offs could be adding a redundant TEXT/CLOB column with the tag data (XML, JSON, other markup/separated format) to TAB_ARTICLES and keeping it in sync with your detail data. By the way, you will really need the M:M schema only if your queries substantiate that. Otherwise, the single table would suffice.
Again, I'd list and evaluate all the criteria first and decide what dimensions really need to be scalable and simplify the rest.
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.
this is more of a question of theory than anything else. I am writing an android app that uses a pre-packaged database. The purpose of the app is solely to search through this database and return values. Ill provide some abstract examples to illustrate my implementation and quandary. The user can search by: "Thing Name," and what I want returned to the user is values a, b, and c. I initially designed the database to have it all contained on a single sheet, and have column 1 be key_index, column 2 be name, column 3 be a, etc etc. When the user searches, the cursor will return the key_index, and then use that to pull values a b and c.
However, in my database "Thing alpha" can have a value a = 4 or a = 6. I do not want to repeat data in the database, i.e. have multiple rows with the same thing alpha, only separate "a" values. So what is the best way to organize the data given this situation? Do I keep all the "Thing Names" in a single sheet, and all the data separately. This is really a question of proper database design, which is definitely something foreign to me. Thanks for your help!
There's a thing called database normalization http://en.wikipedia.org/wiki/Database_normalization. You usually want to avoid redundancy and dependency in the DB entities using a corresponding design with surrogate keys and foreign keys and so on. Your "thing aplpha" looks like you want to have a many-to-many table like e.g. one or many songs belong/s to the same or different genres. You may want to create dictionary tables to hold your id,name pairs and have foreign keys referencing these tables. In your case it will be mostly a read-only DB so you might want to consider creating indexes with high FILLFACTOR percentage don't think sqlite allows it to do though. There're many ways to design the database. Everything depends on the purpose of DB. You can start with a design of your hardware like raids/file systems/db block sizes to match the F-System's block sizes in order to keep the I/O optimal and where to put your tablespaces/filegroups/indexes to balance the i/o load. The whole DB design theory/task is really a deep subject which is not to be underestimated nor is a matter of few sentences in the answer of stackoverflow. :)
without understanding your data better here is my guess at what you are looking for.
table: product
- _id
- name
table: attribute
- product_id
- a
I was wondering if it's possible (it should be) to query multiple tables simultaneously (several at once) in SQLite. Basically I have several tables that have the exact same columns, but the data in them is just organized by the table it's in. I need to be able to use SELECT to get data from the tables (I heard UNION could help), which matches a condition, then group the data by the table it's in.
In other words, would something like this be possible?
SELECT * FROM table1,table2,table3,table4,table5,table6 WHERE day=15 GROUP BY {table}
I'd rather not resort to having to query the tables individually as then I would have a bunch of Cursors that I'd have to manually go through and that would be difficult when I only have one SimpleCursorAdapter? Unless a SimpleCursorAdapter can have several Cursors?
Thanks.
EDIT: The structure of my tables:
Main Table - contains references to subtables in a column "tbls"
and meta-information about the data stored in the subtables
Subtable - contains reference to subsubtables in a column "tbls"
and meta-information about the data stored in the
subsubtables
Subsubtable - contains the actual entries
Basically these tables just make it easier to organize the hierarchical data structure. I suppose instead of having the subsubtables, I could keep the actual entries in the subtable but add a prefix, and have a separate table for the meta-information. It just seems it would be harder to delete/update the structure if I need to remove a level in this data set.
You can create view based on your tables, the query of your view is union of your tables.
create view test as select * from table1 union select * from table2
now you can filter data as you want
for more info check union & view
http://www.w3schools.com/sql/sql_union.asp
http://www.w3schools.com/sql/sql_view.asp
In the end, I decided to forgo having many subsubtables, and instead adding another column like Tim and Samuel suggested. It will probably be more efficient as well then chaining SELECTs with UNION.