I need to add FTS to an existing database.
Started to test external content FTS tables, where the FTS indexes reside in the default (main) DB. Everything worked satisfactorily, except a few things (such as index rebuild) could take considerable amount of time.
Then I read about the possibility to put FTS index into attached DB. This seemed to promise several advantages, hence I decided to give it a try. However, all my trials failed. Here are a few examples:
Situation
We have a table 'account' with a text column 'code', and
Want to create FTS index for that column and place it into separate database file
Test1) ERROR: near ".": syntax error
ATTACH 'ZipFts.sdf' AS ZipFts; CREATE VIRTUAL TABLE ZipFts.account USING fts4(content=account, code);
INSERT INTO ZipFts.account(ZipFts.account) VALUES('rebuild');
Test 2) ERROR: Stack overflow (infinite recursion inside sqlite engine)
ATTACH 'ZipFts.sdf' AS ZipFts; CREATE VIRTUAL TABLE ZipFts.account USING fts4(content=account, code);
INSERT INTO ZipFts.account(account) VALUES('rebuild');
Test3) ERROR: no such table: ZipFts.account
ATTACH 'ZipFts.sdf' AS ZipFts; CREATE VIRTUAL TABLE ZipFts.ZipFts_account USING fts4(content="account", code);
INSERT INTO ZipFts_account(ZipFts_account) VALUES('rebuild');
Test4) ERROR: no such table: ZipFts.main.account
ATTACH 'ZipFts.sdf' AS ZipFts; CREATE VIRTUAL TABLE ZipFts.ZipFts_account USING fts4(content="main.account", code);
INSERT INTO ZipFts_account(ZipFts_account) VALUES('rebuild');
Does anybody know how these things work? Thanks in advance.
After some searching in sqlite3.c I found what might be the answer.
Look at the bottom of the function fts3ReadExprList(). The name of the content table is prefixed with the DB name here! This explains everything.
Moreover, this seems to be the only non-trivial use of zContentTbl (= the name of the content table). When I slightly modified fts3ReadExprList() function as shown in the code underneath, the problem disappeared.
// Code inserted by #JS-->
// Do not prefix zContentTbl with the database name. The table might reside in main database, for example.
if( p->zContentTbl){
fts3Appendf(pRc, &zRet, " FROM '%q' AS x", p->zContentTbl);
}
else
// <--#JS
fts3Appendf(pRc, &zRet, " FROM '%q'.'%q%s' AS x",
...
Note that I did not test the code sufficiently. (So far I only know that the FTS index was created.)
Anyway, for the time being, I consider this an SQLite bug and I'll try to go on with my fix.
I think this is as designed.
If it were otherwise, the underlying table for an external content table could change as databases are attached or detached.
You might be able to achieve this using a contentless FTS Table though.
Dan Kennedy.
Related
I have an Ionic App using SQLite. I don't have any problems with implementation.
The issue is that I need to import an SQL file using SQLitePorter to populate the database with configuration info.
But also, on the same database I have user info, so my question is:
Everytime I start the app, it will import the sql file, fill the database and probably overwrite my user data too? Since it is all on the same base?
I assume that you can always init your table using string queries inside your code. The problem is not that you are importing a .sql file. Right?
According to https://www.sqlitetutorial.net/sqlite-create-table/ it is obvious that you always create a table with [IF NOT EXISTS] switch. Writing a query like :
CREATE TABLE [IF NOT EXISTS] [schema_name].table_name (
column_1 data_type PRIMARY KEY);
you let sqlite to decide if it's going to create a table with the risk to overwrite an existing table. It is supposed that you can trust that sqlite is smart enough, not to overwrite any information especially if you use 'BEGIN TRANSACTION' - 'COMMIT' procedure.
I give my answer assuming that you have imported data and user data in distinct tables, so you can manipulate what you populate and what you don't. Is that right?
What I usually do, is to have a sql file like this:
DROP TABLE configutation_a;
DROP TABLE configutation_b;
CREATE TABLE configutation_a;
INSERT INTO configutation_a (...);
CREATE TABLE configutation_b;
INSERT INTO configutation_b (...);
CREATE TABLE IF NOT EXIST user_data (...);
This means that every time the app starts, I am updating with the configuration data I have at that time (that's is why we use http.get to get any configuration file from a remote repo in the future) and create user data only if user_data table is not there (hopefully initial start).
Conclusion: It's always a good practice, in my opinion, to trust a database product 100% and abstractly let it do any transaction that might give you some risk if you implemented your self in your code; since it gives a tool for that.For example, the keyword [if not exists], is always safer than implementing a table checker your self.
I hope that helps.
PS: In case you refer in create database procedure, SQLite, connects to a database file and it doesn't exist, it creates it. For someone comfortable in sqlite command line, when you type
sqlite3 /home/user/db/configuration.db will connect you with this db and if the file is not there, it will create it.
I'm trying to use RJDBC to connect to a SAP HANA database and query for a temporary table, which is stored with a #-prefix:
test <- dbGetQuery(jdbcConnection,
"SELECT * FROM #CONTROL_TBL")
# Error in [...]: invalid table name: Could not find table/view #CONTROL_TBL in schema USER
If I execute the SQL statement in HANA, it works perfectly fine. I'm also able to query for permanent tables. Therefore I assume that R doesn't pass over the hashtag. Inserting escapes like "SELECT * FROM \\#CONTROL_TBL" however didn't solve my problem.
It's not possible to query for the data of a local or global temporary table from a different session, since they are by definition session-specific. In the case of a global temporary table one can query for the metadata of the table because they are shared across sessions.
Source: Tutorial for HANA temporary tables
You have to double-quote the table because it contains special characters, see SAP Help, identifiers for details.
test <- dbGetQuery(jdbcConnection,
'SELECT * FROM "#CONTROL_TBL"')
See also related discussion on stackoverflow.
Ok, local temporary tables are always only visible to the session in which they've been defined, while global temporary tables are visible just like normal tables, but the data is session private.
So, if you created the local temp. table (name starts with #) in a different session, then no wonder it cannot be found.
For your example, the question is: why do you need a temporary table in the first place?
Instead of that, you could e.g. define a view or a table function to select data from.
I need to parameterize a view, and I am doing so by creating a TEMP TABLE which has the parameters for the view.
CREATE TEMP TABLE parms (parm1 INTEGER, parm2 INTEGER);
CREATE VIEW tableview AS ...
The VIEW is rather complex, but it basically uses these two parameters to kick start a recursive CTE, and there isn't any other way that I have found to express the view without these parameters.
The parameters must be stored in a temporary table because each connection should be able to have its own view with different parameters.
In any case, this works fine for creating the view itself, so long as I create the same TEMP TABLE at the start of any queries that use the view, e.g.:
CREATE TEMP TABLE parms (parm1 INTEGER, parm2 INTEGER);
INSERT INTO parms (parm1,parm2) VALUES (5,66);
SELECT * FROM tableview;
I am able to do the same thing to create a trigger to allow inserts on the view:
CREATE TEMP TABLE parms (parm1 INTEGER, parm2 INTEGER);
CREATE TRIGGER tableinsert INSTEAD OF INSERT ON tableview ...
However, when I try to do an actual INSERT (re-creating the TEMP TABLE first as before) I get an error:
no such table: main.parms
If I create a non-temporary table, I do not get this error, but then I have the problem that different connections can't have their own separate views.
I have review the documentation for triggers, and it mentions caveats of using temporary triggers on a non-temporary table, but I don't see anything regarding the reverse.
I did find a reference elsewhere that indicated that "the table... must exist in the same database as the table or view to which the trigger is attached". I thought a temporary table was part of the current database, is this not true? Is there some way to make this true?
I also tried accessing the parms table as temp.parms in the TRIGGER, but got the error:
qualified table names are not allowed on INSERT, UPDATE, and DELETE
statements within triggers
If I can't use a temporary table, is there some way to work around it to accomplish the same thing?
Update: Ok, so it seems to be an SQLite limitation. After digging around a bit in the SQLite source code, it seems to be pretty trivial to allow SELECT access to a temporary table in a trigger. However, allowing UPDATE access appears to be a lot harder.
Temporary objects are created in a separate database named temp, so they are not accessible from triggers in other databases.
The remaining mechanism to get a connection-specific value into a trigger is to use a user-defined function.
I have a .sqlite db which contains only one table. That table contains three columns and I am interested in indexing one column ONLY.
The problem is, when I perform the indexing, I got an empty index table !
I am using SQLite Manager add-ons for Firefox. This is the syntax that appears before I confirm the indexing:
CREATE INDEX "main"."tableIndex" ON "table" ("column1" ASC)
I don't know what is the problem here. I tried this tool - long time ago - with another database and it works fine.
Any suggestion ?
You cannot "see" the contents of a database index. No table or table-like structure is created that corresponds to the index. So there is nothing to look at that could be empty.
If the CREATE INDEX command ran without error, you can be confident that the index was created and will continue to be maintained by SQLite as you add, remove, and update data.
As per the comments, below, #iturki is actually trying to index for full text search. SQLite supports several extensions for full text search but they are not implemented through the stanard CREATE INDEX command. See this reference.
Try use VACUUM query. It will completely rebuild sqlite database file and will rebuild all indices and reset all ROWID etc.
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.