I am aggregating numbers from different sqlite databases into a single output database table.
I need to add up integer columns i1,i2,i3 in the output table based on three indicating columns a,b,c that tell me which rows to update:
ATTACH DATABASE "out.db" AS output;
INSERT INTO output.rows(a,b,c,i1,i2,i3)
SELECT DISTINCT "some_value", b, c, 0, 0, 0 FROM main.rows
ON CONFLICT IGNORE;
#THE FOLLOWING LINES MIGHT SHOW WHAT I MEAN...
UPDATE output.rows SET i1=i1+i1_,i2=i2+i2_, i3=i3+i3_
WHERE a="some_value" AND b=b_ and c=c_
SELECT i1_, i2_, i3_, b_, c_ FROM main.rows;
I do not want to type in all the combinations of a,b,c. As you can see, a does not come from main but from external information (the filename).
In newer versions of SQLite that support UPSERT, the following seems to work:
ATTACH DATABASE "$out.db" AS output;
INSERT INTO output.rows(a,b,c,i1,i2,i3)
SELECT "some_value", b, c, i1, i2, i3 FROM main.rows WHERE true
ON CONFLICT (a,b,c) DO UPDATE SET i1=i1+i1, i2=i2+i2, i3=i3+i3;
In my case, the columns i1,i2,i3 coming from main actually had a different name (say I1,I2,I3) than their counterpart in output, therefore the UPDATE was clearer (i1=i1+I1). I failed to reference as main.rows.i1 inside the UPDATE statement. If you know how to solve that ambiguity, please comment.
Related
I have a database that has two integer columns, and I'm trying to find a way to select the top 'x' amount of rows with the highest sums of these two columns. I'm trying to eliminate the need of creating a third column that stores the sum of the two, unless there's a way to to automatically update this column every time one of the other two are altered. I'm using SQLite by the way, as I know there are some slight differences here and there between SQL/SQLite syntax.
Any help is appreciated.
Something like
SELECT a, b
FROM yourtable
ORDER BY a + b DESC
LIMIT :x
should do it.
I have a table t with around 500,000 rows. One of the columns (stringtext) contains a very long string and I have now discovered that that there are in fact only 80 distinct strings. I'd like to declutter table t by moving the strings into a separate table, s, and merely referencing them in t.
I have created a separate table of the long strings, including what is effectively an explicit row-index number using:
CREATE TEMPORARY TABLE stmp AS
SELECT DISTINCT
stringtext
FROM t;
CREATE TABLE s AS
SELECT _ROWID_ AS stringindex, stringtext
FROM stmp;
(It was creating this table that showed me there were only a few distinct strings).
How can I now replace stringtext in t with the corresponding stringindex from s?
I would think about something like Update t set stringtext = (select stringindex from s where s.stringtext = t.stringtext) and would recommend first making an index on s(stringtext) as SQLite might not be smart enough to build a temporary index. And then a VACUUMing would be in order.
Untested.
Okay, I've 2 tables. One is called users2 and one is called user_totals. ive rows that are called clicks(impression_count), fclicks(use_count), completed_stus(completion_count). the ones in braces are the new ones in the user_totals table. Anyway I'd like to add all the ints from the first table into the second table but only if the stats in the second table are 0. also it should be added to the same user id which is id in the first table and user_id in the second. Could somebody give me a working mysqli statement to perform that ?
You can create a insert with select:
INSERT INTO x
(a, b, c, d)
SELECT a, b, c, d
FROM y
WHERE z=2
I am trying to populate everyrow in a column with random ranging from 0 to row count.
So far I have this
UPDATE table
SET column = ABS (RANDOM() % (SELECT COUNT(id) FROM table))
This does the job but produces duplicate values, which turned out to be bad. I added a Unique constraint but that just causes it to crash.
Is there a way to update a column with random unique values from certain range?
Thanks!
If you want to later read the records in a random order, you can just do the ordering at that time:
SELECT * FROM MyTable ORDER BY random()
(This will not work if you need the same order in multiple queries.)
Otherwise, you can use a temporary table to store the random mapping between the rowids of your table and the numbers 1..N.
(Those numbers are automatically generated by the rowids of the temporary table.)
CREATE TEMP TABLE MyOrder AS
SELECT rowid AS original_rowid
FROM MyTable
ORDER BY random();
UPDATE MyTable
SET MyColumn = (SELECT rowid
FROM MyOrder
WHERE original_rowid = MyTable.rowid) - 1;
DROP TABLE MyOrder;
What you seem to be seeking is not simply a set of random numbers, but rather a random permutation of the numbers 1..N. This is harder to do. If you look in Knuth (The Art of Computer Programming), or in Bentley (Programming Pearls or More Programming Pearls), one suggested way is to create an array with the values 1..N, and then for each position, swap the current value with a randomly selected other value from the array. (I'd need to dig out the books to check whether it is any arbitrary position in the array, or only with a value following it in the array.) In your context, then you apply this permutation to the rows in the table under some ordering, so row 1 under the ordering gets the value in the array at position 1 (using 1-based indexing), etc.
In the 1st Edition of Programming Pearls, Column 11 Searching, Bentley says:
Knuth's Algorithm P in Section 3.4.2 shuffles the array X[1..N].
for I := 1 to N do
Swap(X[I], X[RandInt(I,N)])
where the RandInt(n,m) function returns a random integer in the range [n..m] (inclusive). That's nothing if not succinct.
The alternative is to have your code thrashing around when there is one value left to update, waiting until the random number generator picks the one value that hasn't been used yet. As a hit and miss process, that can take a while, especially if the number of rows in total is large.
Actually translating that into SQLite is a separate exercise. How big is your table? Is there a convenient unique key on it (other than the one you're randomizing)?
Given that you have a primary key, you can easily generate an array of structures such that each primary key is allocated a number in the range 1..N. You then use Algorithm P to permute the numbers. Then you can update the table from the primary keys with the appropriate randomized number. You might be able to do it all with a second (temporary) table in SQL, especially if SQLite supports UPDATE statements with a join between two tables. But it is probably nearly as simple to use the array to drive singleton updates. You'd probably not want a unique constraint on the random number column while this update is in progress.
So I know enough SQL just to be really dangerous (I don't normally work the back-end) but cannot get the following view to be created successfully ;) The result set I'm after is a data set that has rows assigned as a column alias from multiple tables (instead of a 1xN flat of all columns). There is a many-to-one relationship when looking at the main table, based on foreign keys associated to the row id of the appropriate related table.
Ideally I'd like a data set that looks like this in the return:
dataset.transaction_row[n]: col1, col2, col3, coln... (columns from the transaction table)
dataset.category_row[n]: col1, co2, col3, coln... (columns from the category table)
and so on...
I get the following error:
Query Error: near "AS": syntax error Unable to execute statement
From:
CREATE VIEW view_unreconciled_transactions
AS SELECT account_transaction.* AS transaction_row,
category.* AS category_row,
memorized.name_rule_replace OR account_transaction.name AS payee
FROM account_transaction
LEFT JOIN memorized ON account_transaction.memorized_key = memorized.id
LEFT JOIN category ON account_transaction.category_key = category.id
WHERE status != 2
ORDER BY account_transaction.dt_posted DESC
It seems easy enough since the result-column selector is repeatable which includes expressions (referencing sqlite's syntax diagrams). In reference to the error, I'm assuming it's complaining about the 2nd 'AS' where I'm trying to get table.* assigned as an alias. Any help in the right direction is appreciated. If I had to, I suppose I could explicitly state all columns but that feels like a kludge.
The AS modifier can only be applied to a single column, not to a collection such as the * you used. You will have to break them out into specific names, (which is best practice IMHO anyway)
It looks like you want to make a "pivot table". They can be tricky to make in a database. I can say that if you a data result, where each row comes from a different table source, and the columns form each table are IDENTICAL, then you could try using a UNION statement to join the different results together like they are just one dataset.
NOTE that the columns all take their naming cue from the first dataset in a UNION and the datatype all need to be the same.