I'm currently trying to create an Flashcard application, in which the user can either create his own cards/notes or use pre-defined cards. The idea is to have around 500 to 1000 cards to be inserted on the database right after its creation. But how do I insert this initial data?
The only solution I could come up with is creating each one of the cards inside the "onCreate()" method of my "SQLiteOpenHelper" class, which would lead to repeating 500+ times the insert process:
db.execSQL("INSERT INTO table (column1, column2, columnN) VALUES(...)");
Is it the right thing to do? Would it work, and if so is it a good method or would I have any problems by doing it this way?
Related
I'd like to use flyway for a DB update with the situation that an DB already exists with productive data in it. The problem I'm looking at now (and I did not find a nice solution yet), is the following:
There is an existing DB table with numeric IDs, e.g.
create table objects ( obj_id number, ...)
There is a sequence "obj_seq" to allocate new obj_ids
During my DB migration I need to introduce a few new objects, hence I need new
object IDs. However I do not know at development time, what ID
numbers these will be
There is a DB trigger which later references these IDs. To improve performance I'd like to avoid determine the actual IDs every time the trigger runs but rather put the IDs directly into the trigger
Example (very simplified) of what I have in mind:
insert into objects (obj_id, ...) values (obj_seq.nextval, ...)
select obj_seq.currval from dual
-> store this in variable "newID"
create trigger on some_other_table
when new.id = newID
...
Now, is it possible to dynamically determine/use such variables? I have seen the flyway placeholders but my understanding is that I cannot set them dynamically as in the example above.
I could use a Java-based migration script and do whatever string magic I like - so, that would be a way of doing it, but maybe there is a more elegant way using SQL?
Many thx!!
tge
If the table you are updating contains only reference data, get rid of the sequence and assign the IDs manually.
If it contains a mix of reference and user data, you need to select the id based on values in other columns.
I am using a global application user account to access database A. This user account does not have permissions to modify database A's schema (ie, create tables, modify tables, etc). This user also has access to database B, but only views. I need to run SQL to feed data from a view in database B into a table in database A.
In a perfect world, I would be able to use this SQL:
create database_a.mytable as (select * from database_b) with no data
However, the user can't create tables in database A. If I could get the DDL of the select statement then I could log in under my personal account (which doesn't have any access to database B) and run the DDL in database A to create the table.
The only other option is to manually write the SQL, but I don't want to do that, especially since this view I am wanting to copy has many columns of varying data types and sizes.
Edit: I may be getting closer. I just experimented with this:
show (select * from database_b.myview)
However, it generated the DLL of every single table that is used in the view itself, as well as the definition for the view. This doesn't really help me since I just want the schema of the select statement itself. In other words, I need what would be generated if I were to use the create table as statement mentioned above.
Edit for Rob: Perhaps "DDL" was the wrong term to use. Using show view db.myview just shows the definition of the view, not the schema it represents. In my above example of create table as, I show how you can create a table that mimics the schema of a result set returned in a select. It generates a DDL on the back end for creating a table and then executes that DDL to actually create the table. You can then say show table db.newtable and see the new table's DDL. I want to get that DDL directly from a select statement so that I can copy it, log out of the app account, into my personal account, and then execute the DDL to create the table.
This is only to save me the headache of having to type out the DDL manually by hand to save time and reduce typing errors, especially since the source view has so many columns. That said, I think hitting up the DBA or writing some snazzy stored procedure to do dynamic stuff would be a bit over the top for my needs. I think there has to be a way to get the DDL for creating a table schema directly from a select statement.
Generate DDL Statements for objects:
SHOW TABLE {DatabaseB}.{Table1};
SHOW VIEW {DatabaseB}.{View1};
Breakdown of columns in a view:
HELP VIEW {DatabaseB}.{View1};
However, without the ability to create the object in the target database DatabaseA your don't have much leverage. Obviously, if the object already existed INSERT INTO SELECT ... FROM DatabaseB.Table1 or MERGE INTO would be options that you already explored.
Alternative Solution
Would it be possible to have a stored procedure created that dynamically created the table based on the view name that is provided? The global application account would simply need privilege to execute the procedure. Generally the user creating the stored procedure would need the permissions to perform the actions contained within the stored procedure. (You have some additional flexibility with this in Teradata 13.10.)
There are some caveats with this approach. You are attempting to materialize views that could reference anywhere from hundreds to billions of records. These aren't simple 1:1 views that are put on top of the target tables. Trying to determine the required space in the target database to materialize the view will be difficult. Performance can and will vary depending on the complexity of the view and the data volumes. This will not be a fast-path or data block optimized operation.
As a DBA, I would be concerned with this approach being taken on by a global application account without fully understanding the intent. I trust you have an open line of communication with the DBA(s) involved for supporting this system. I'm sure there are reasons for your madness that can't be disclosed here.
Possible Solution - VOLATILE TABLE
Unless the implicit privilege for CREATE TABLE has been revoked from the global application account this solution should work.
Volatile tables do not require perm space. There table definitions persist for the duration of the session and any data inserted into them relies on the spool space of the user who instantiated it.
CREATE VOLATILE TABLE {Global Application UserID}.{TableA_Copy} AS
(
SELECT *
FROM {DatabaseB}.{TableA}
)
WITH NO DATA
NO PRIMARY INDEX
ON COMMIT PRESERVE ROWS;
SHOW TABLE {Global Application UserID}.{TableA_Copy};
I opted to use a Teradata 13.10 feature called NO PRIMARY INDEX. By default, CREATE TABLE AS will take the first column of the SELECT statement and make it the PRIMARY INDEX of the table. This could lead to skewing and perm space issues in your testing depending on the data demographics. You can specify an explicit PRIMARY INDEX on your own as you understand the underlying data. (See the DDL manuals for details on the syntax if you're uncertain.)
The use of ON COMMIT PRESERVE ROWS for the intent of this example is probably extraneous. But in reality if you popped any data into that table for testing this clause would be beneficial in Teradata mode as the data would otherwise be lost immediately after the CREATE TABLE or any other data manipulation was performed against the volatile table.
I have a table where I store relations between two other table with a float indicating relevance between the two rows. I have unique key on the two reference columns. The problem is, that I have to rebuild it regularly, which is kinda lengthy. So, I can't just truncate the table while I'm doing so, but I can't insert the relevance for the same row while they would be duplicates either. That's why I thought it would be great to save the current timestamp to a variable, persist the relations with REPLACE INTO instead of INSERT INTO and then remove everything created before the saved timestamp. However, I couldn't find out how. Any idea? I'm using Doctrine 2.2.0-DEV and Symfony 2.1.0-DEV.
Doctrine 2 doesn't support INSERT REPLACE or UPSERT, sorry.
I have a table in a MS Access 2010 Database and it can easily be split up into multiple tables. However I don't know how to do that and still keep all the data linked together. Does anyone know an easy way to do this?
I ended up just writing a bunch of Update and Append queries to create smaller tables and keep all the data synced.
You must migrate to other database system, like MSSQL, mySQL. You can't do in MsAccess replication...
Not sure what do you mean by split up into multiple tables.
Are the two tables have same structure? you want to divide the table into two pats ... means if original table has fields A,B,C,D ... then you want to split it to Table1: A,B and
Table2: C,D.
Anyways, I googled it a bit and the below links might of what you are looking for. Check them.
Split a table into related tables (MDB)
How hard is it to split a table in Access into two smaller tables?
Where do you run into trouble with the table analyzer wizard? Maybe you can work around the issue you are running into.
However, if the table analyzer wizard isn't working out, you might also consider the tactics described in http://office.microsoft.com/en-us/access-help/resolve-and-help-prevent-duplicate-data-HA010341696.aspx.
Under Microsoft Access 2012, Database Tools, Analyze table.. I use the wizard to split a large table into multiple normalized tables. Hope that helps.
Hmmm, can't you just make a copy of the table, then delete opposite items in each table leaving the data the way you want except, make sure that both tables have the same exact auto number field, and use that field to reference the other.
It may not be the most proficient way to do it, but I solved a similar issue the following way:
a) Procedure that creates a new table via SQL:
CREATE TABLE t002 (ID002 INTEGER PRIMARY KEY, CONSTRAINT SomeName FOREIGN KEY (ID002) REFERENCES t001(ID001));
The two tables are related to each other through the foreign key.
b) Procedure that adds the neccessary fields to the new table (t002). In the following sample code let's use just one field, and let's call it [MyFieldName].
c) Procedure to append all values of field ID001 from Table t001 to field ID002 in Table t002, via SQL:
INSERT INTO ID002 (t002) SELECT t001.ID001 FROM t001;
d) Procedure to transfer values from fields in t001 to fields in t001, via SQL:
UPDATE t001 INNER JOIN t002 ON t001.ID001 = t002.ID002 SET t002.MyFieldName = t001.MyFieldName;
e) Procedure to remove (drop) the fields in question in Table t001, via SQL:
ALTER TABLE t001 DROP COLUMN MyFieldName;
f) Procedure that calls them all one after the other. Fieldnames are fed into the process as parameters in the call to Procedure f.
It is quite a bunch of coding, but it did the job for me.
I need to modify a column in a SQLite database but I have to do it programatically due to the database already being in production. From my research I have found that in order to do this I must do the following.
Create a new table with new schema
Copy data from old table to new table
Drop old table
Rename new table to old tables name
That seems like a ridiculous amount of work for something that should be relatively easy. Is there not an easier way? All I need to do is change a constraint on a existing column and give it a default value.
That's one of the better-known drawbacks of SQLite (no MODIFY COLUMN support on ALTER TABLE), but it's on the list of SQL features that SQLite does not implement.
edit: Removed bit that mentioned it may being supported in a future release as the page was updated to indicate that is no longer the case
If the modification is not too big (e.g. change the length of a varchar), you can dump the db, manually edit the database definition and import it back again:
echo '.dump' | sqlite3 test.db > test.dump
then open the file with a text editor, search for the definition you want to modify and then:
cat test.dump | sqlite3 new-test.db
As said here, these kind of features are not implemented by SQLite.
As a side note, you could make your two first steps with a create table with select:
CREATE TABLE tmp_table AS SELECT id, name FROM src_table
When I ran "CREATE TABLE tmp_table AS SELECT id, name FROM src_table", I lost all the column type formatting (e.g., time field turned into a integer field
As initially stated seems like it should be easier, but here is what I did to fix. I had this problem b/c I wanted to change the Not Null field in a column and Sqlite doesnt really help there.
Using the 'SQLite Manager' Firefox addon browser (use what you like). I created the new table by copying the old create statement, made my modification, and executed it. Then to get the data copied over, I just highlighted the rows, R-click 'Copy Row(s) as SQL', replaced "someTable" with my table name, and executed the SQL.
Various good answers already given to this question, but I also suggest taking a look at the sqlite.org page on ALTER TABLE which covers this issue in some detail: What (few) changes are possible to columns (RENAME|ADD|DROP) but also detailed workarounds for other operations in the section Making Other Kinds Of Table Schema Changes and background info in Why ALTER TABLE is such a problem for SQLite. In particular the workarounds point out some pitfalls when working with more complex tables and explain how to make changes safely.