I have the following columns in a SQLite DB.
id,ts,origin,product,bid,ask,nextts
1,2016-10-18 20:20:54.733,SourceA,Dow,1.09812,1.0982,
2,2016-10-18 20:20:55.093,SourceB,Oil,7010.5,7011.5,
3,2016-10-18 20:20:55.149,SourceA,Dow,18159.0,18161.0,
How can I populate the 'next timestamp' column (nextts) with the next timestamp for the same product (ts), from the same source? I've been trying the following, but I can't seem to put a subquery in an UPDATE statement.
UPDATE TEST a SET nextts = (select ts
from TEST b
where b.id> a.id and a.origin = b.origin and a.product = b.product
order by id asc limit 1);
If I call this, I can display it, but I haven't found a way of updating the value yet.
select a.*,
(select ts
from TEST b
where b.id> a.id and a.origin = b.origin and a.product = b.product
order by id asc limit 1) as nextts
from TEST a
order by origin, a.id;
The problem is that you're using table alias for table in UPDATE statement, which is not allowed. You can skip alias from there and use unaliased (but table-name prefixed) reference to its columns (while keeping aliased references for the SELECT), like this:
UPDATE TEST
SET nextts = (
SELECT b.ts
FROM TEST b
WHERE b.id > TEST.id AND
TEST.origin = b.origin AND
TEST.product = b.product
ORDER BY b.id ASC
LIMIT 1
);
Prefixing unaliased column references with the table name is necessary for SQLite to identify that you're referencing to unaliased table. Otherwise the id column whould be understood as the id from the closest[*] possible data source, in which case it's the aliased table (as b alias), while we're interested in the unaliased table, therefore we need to explicitly tell SQLite that.
[*] Closest data source is the one listed in the same query, or parent query, or parent's parent query, etc. SQLite is looking for the first data source (going from inner part to the outside) in the query hierarchy that defines this column.
Related
I need to merge some randomly uppercased data that has been collected in an SQLite table key_val, such that key is always lowercase and no vals are lost. There is a unique compound index on key,val.
The initial data looks like this:
key|val
abc|1
abc|5
aBc|1
aBc|5
aBc|3
aBc|2
AbC|1
abC|3
The result after the merge would be
key|val
abc|1
abc|2
abc|3
abc|5
In my programmer brain, I would
for each `key` with upper case letters;
if a lower cased `key` is found with the same value
then delete `key`
else update `key` to lower case
Re implementing the loop has a sub query for each row found with upper case letters, to check if the val already exists as a lower case key
If it does, I can delete the cased key.
From there I can UPDATE key = lower(key) as the "duplicates" have been removed.
The first cut of the programming method of finding the dupes is:
SELECT * FROM key_val as parent
WHERE parent.key != lower(parent.key)
AND 0 < (
SELECT count(s.val) FROM key_val as s
WHERE s.key = lower(parent.key) AND s.val = parent.val
)
ORDER BY parent.key DESC;
I'm assuming there's a better way to do this in SQLite? The ON CONFLICT functionality seems to me like it should be able to handle the dupe deletion on UPDATE but I'm not seeing it.
First delete all the duplicates:
DELETE FROM key_val AS k1
WHERE EXISTS (
SELECT 1
FROM key_val AS k2
WHERE LOWER(k2.key) = LOWER(k1.key) AND k2.val = k1.val AND k2.rowid < k1.rowid
);
by keeping only 1 combination of key and val with the min rowid.
It is not important if you kept the key with all lower chars or not, because the 2nd step is to update the table:
UPDATE key_val
SET key = LOWER(key);
See the demo.
Honestly it might just be easier to create a new table and then insert into it. As it seems you really just want a distinct select here, use:
INSERT INTO kev_val_new ("key", val)
SELECT DISTINCT LOWER("key"), val
FROM key_val;
Once you have populated the new table, you may drop the old one, and then rename the new one to the previous name:
DROP TABLE key_val;
ALTER TABLE key_val_new RENAME TO key_val;
I agree with #Tim that it would be easire to re-create table using simple select distict lower().. statement, but that's not always easy if table has dependant objects (indexes, triggers, views). In this case this can be done as sequence of two steps:
insert lowered keys which are not still there:
insert into t
select distinct lower(tr.key) as key, tr.val
from t as tr
left join t as ts on ts.key = lower(tr.key) and ts.val = tr.val
where ts.key is null;
now when we have all lowered keys - remove other keys:
delete from t where key <> lower(key);
See fiddle: http://sqlfiddle.com/#!5/84db50/11
However this method assumes that key is always populated (otherwise it would be a strange key)
If vals can be null then "ts.val = tr.val" should be replaced with more complex stuff like ifnull(ts.val, -1) = ifnull(tr.val, -1) where -1 is some unused value (can be different). If we can't assume any unused value like -1 then it should be more complex check for null / not null cases.
Hello i have an sqlite db with many records like 10540 record they are ordered by creation time , i want to shift like a record in the middle and like to do it automatically
for example :
select * from table1 where id >= 8521;
UPDATE Table1 SET id = id +1 ;
does not work i get Error: Result: UNIQUE constraint failed:
so i want to shift up all records from 8521 to the last record and get place in the 8520 place for example so i can insert my record in that place of table .
even the
id = select max(id)+1
does not work how can i increment the id from last record to the needed record so i can put a place in the records db
A simple update statement would fail, as it would try to create duplicate values in the primary key.
What you can do is this:
First update the column to the negatives of the values they should have:
update table1
set id = -(id + 1)
where id > 8520;
Now there are no duplicates and you just need to update again to the positive values:
update table1
set id = -id
where id < 0;
This will do the trick, but any kind of updating the primary key is not a recommended practice
Edit
I would rather explicitly state my problem I'm facing rather than assuming the approach. There could be an easiest solution to my problem.
I need to select records by joining two different table based on the result from another table. And I have to use different joins based on the result from the first table.
If a particular record is present in the first table, I have two use inner join the first table whereas if it's not present, then I have to left join.
bool recordPresent = select exists (select * from firstTable where access_id = 13) as access
if (recordPresent)
results = select * from secondTable s left join firstTable f on f.access_id = s.access_id where f.access_id is null order by access_id
else
results = select * from secondTable s inner join firstTable f on f.access_id = s.access_id
I'm having a difficult time getting the UPDATE command in Sqlite to update all records with a new value it finds in another table using a subquery select statement. It incorrectly updates every column in Table1 with the first value it finds in column Table2.
When I run the select portion of the query alone it runs fine and returns all the proper values. It basically looks up the nearest value in multiples of 300000 from a lookup table called Adjustment.
code:
Update TEMP1
set New_position =
(
select (Temp1.Col1 + Adjustment.Offset) as NewValue
from Adjustment, TEMP1
where Adjustment.LookupValue = cast(TEMP1.Col1 / 300000 as Int) * 300000
)
You are trying to use a correlated subquery:
A SELECT statement used as either a scalar subquery or as the right-hand operand of an IN, NOT IN or EXISTS expression may contain references to columns in the outer query. Such a subquery is known as a correlated subquery. A correlated subquery is reevaluated each time its result is required. An uncorrelated subquery is evaluated only once and the result reused as necessary.
But your subquery does not actually contain a reference to columns in the outer query; the FROM Temp1 in the inner query is a new instance of the Temp1 table, and Temp1.Col1 refers to that. The value of Temp1.Col1 is from some random row in Temp1.
Just drop the Temp1 from the FROM clause:
UPDATE Temp1
SET New_position = (SELECT Temp1.Col1 + Adjustment.Offset
FROM Adjustment
WHERE LookupValue = CAST(Temp1.Col1 / 300000 AS INT) * 300000);
I have a MySQL table Page with 2 columns: PageID and OrderByMethod.
I also then have a Data table with lots of columns including PageID (the Page the data is on), DataName, and DataDate.
I want OrderByMethod to have one of three entries: Most Recent Data First, Most Recent Data Last, and Alphabetically.
Is there a way for me to tack an "ORDER BY" clause to the end of this query that will vary its ordering method based on the contents of the "OrderByMethod" column? For example, in this query, I would want to have the ORDER BY clause contain whatever ordering rule is stored in Page 1's OrderByMethod column.
GET * FROM `Data` WHERE `Data`.`PageID`=1 ORDER BY xxxxxx;
Maybe a SELECT clause in the ORDER BY clause? I'm not sure how that would work though.
Thanks!
select Data.*
from Data
inner join Page on (Data.PageID=Page.PageID)
where Data.PageID=1
order by
if(Page.OrderByMethod='Most Recent Data First', now()-DataDate,
if(Page.OrderByMethod='Most Recent Data Last', DataDate-now(), DataName)
);
You can probably do this with the IF syntax to generate a column that you can then order by.
SELECT *, IF(Page.OrderBy = 'Alphabetically', Data.DataName, IF(Page.OrderBy = 'Most Recent Data First', NOW() - Data.DataDate, Data.DataDate - NOW())) AS OrderColumn
FROM Data
INNER JOIN Page ON Data.PageID = Page.PageID
WHERE Page.PageID = 1
ORDER BY OrderColumn
The direction of the ordering is determined in the calculation of the data instead of specifying a direction in the ORDER BY
Can you just append the order by clause to the select statement and rebind the table on postback?
If you want to use the content of the column in Page table as an expression in ORDER BY you have to do it using prepared statements. Let say, you store in OrderByMethod something like "field1 DESC, field2 ASC" and you want this string to be used as it is:
SET #order_by =(SELECT OrderByMethod FROM Page WHERE id = [value]);
SET #qr = CONCAT(your original query,' ORDER BY ', #order_by);
PREPARE stmt FROM #qr;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
If you want the result set to be sorted based on the value of OrderByMethod , you can use IF as it was already mentioned by others, or CASE :
...
ORDER BY
CASE OrderByMethod
WHEN 'val1' THEN field_name1
WHEN 'val2' THEN field_name2
....etc
END