Need to modify the data in an SQLite database that has fields similar to:
hash (string)
modTime (long, time in ms)
data (any data, e.g. string)
I know the hash value of the record to set the data for (it's really xxHash of some binary blob). There can be several records with the same hash, but I need to modify only the one with MAX(modTime) value with the matching hash... Can't figure out how to construct the UPDATE command.
You can use NOT EXISTS in the WHERE clause:
UPDATE tablename
SET data = new_data
WHERE hash = ?
AND NOT EXISTS (SELECT 1 FROM tablename t WHERE t.hash = tablename.hash AND t.modTime > tablename.modTime)
Or use the column rowid to find the row that you want to update:
UPDATE tablename
SET data = new_data
WHERE rowid = (SELECT rowid FROM tablename WHERE hash = ? ORDER BY modTime DESC LIMIT 1)
or with FIRST_VALUE() window function:
UPDATE tablename
SET data = new_data
WHERE rowid = (SELECT DISTINCT FIRST_VALUE(rowid) OVER (ORDER BY modTime DESC) FROM tablename WHERE hash = ?)
Replace new_data with the new value of data and ? with the value of hash you search for.
Related
I'm trying to replace a placeholder string inside a selection of 10 random records with a random string (a name) taken from another table, using only sqlite statements.
i've done a subquery in order to replace() of the placeholder with the results of a subquery. I thought that each subquery loaded a random name from the names table, but i've found that it's not the case and each placeholder is replaced with the same string.
select id, (replace (snippet, "%NAME%", (select
name from names
where gender = "male"
) )
) as snippet
from imagedata
where timestamp is not NULL
order by random()
limit 10
I was expecting for each row of the SELECT to have different random replacement every time the subquery is invoked.
hello i'm %NAME% and this is my house
This is the car of %NAME%, let me know what you think
instead each row has the same kind of replacement:
hello i'm david and this is my house
This is the car of david, let me know what you think
and so on...
I'm not sure it can be done inside sqlite or if i have to do it in php over two different database queries.
Thanks in advance!
Seems that random() in the subquery is only evaluated once.
Try this:
select
i.id,
replace(i.snippet, '%NAME%', n.name) snippet
from (
select
id,
snippet,
abs(random()) % (select count(*) from names where gender = 'male') + 1 num
from imagedata
where timestamp is not NULL
order by random() limit 10
) i inner join (
select
n.name,
(select count(*) from names where name < n.name and gender = 'male') + 1 num
from names n
where gender = 'male'
) n on n.num = i.num
I know it works with following code in MySQL to achieve such goal:
set #n = 0;
select (#n := #n + 1),test_score from test_score where student_name = 'Gao' and test_subject = 'math'
In SQLite,there is no variable, so how can I implement similar function in SQLite?
Thanks!
Assuming you have an ID field in your test_score table you could just easily add ORDER BY ID ASC to your select query.
CREATE TABLE test_score (ID INTEGER AUTOINCREMENT, student_name TEXT, test_subject TEXT, score TEXT)
SELECT ID, score FROM test_score WHERE student_name='Gao' AND test_subject='math' ORDER BY ID ASC;
NB: by default the query would be ordered by the ID anyway, but in case you would want to switch it to the most recent just replace ASC with DESC
I want to add data to table STATISTICS using INSERT statements.
I also want to move new counts to old counts and new date to old date as the new data comes in.
This is where it gets lil tricky because I don't know if there is such a thing as INSERT INTO table with SET in Oracle.
INSERT INTO STATISTICS
SET
MODEL = '&MY_MODEL',
NEW_COUNT =
(
SELECT COUNT(*)
FROM TABLE CLIENTS
),
NEW_DATE = SYSDATE,
OLD_COUNT = NEW_COUNT,
OLD_DATE = NEW_DATE,
PRNCT_CHANGE = ((NEW_COUNT) - (OLD_COUNT)) / (NEW_COUNT)*100
);
How do I accomplish this in Oracle?
This should upsert statistics, adding new ones as you go. It presumes a unique key on MODEL; if that's not true, then you'd have to do inserts as Angelina said, getting only the most recent row for a single MODEL entry.
MERGE INTO STATISTICS tgt
using (SELECT '&MY_MODEL' AS MODEL,
(SELECT COUNT(*) FROM CLIENTS) AS NEW_COUNT,
SYSDATE AS DATE_COUNT,
NULL AS OLD_COUNT,
NULL OLD_DATE,
NULL AS PRCNT_CHANGE
FROM DUAL) src
on (TGT.MODEL = SRC.MODEL)
WHEN MATCHED THEN UPDATE
SET TGT.NEW_COUNT = SRC.NEW_COUNT,
TGT.NEW_DATE = SRC.NEW_DATE,
TGT.OLD_COUNT = TGT.NEW_COUNT,
TGT.OLD_DATE = TGT.NEW_DATE,
TGT.PRCNT_CHG = 100 * (SRC.NEW_COUNT - TGT.NEW_COUNT) / (SRC.NEW_COUNT)
-- NEEDS DIV0/NULL CHECKING
WHEN NOT MATCHED THEN INSERT
(MODEL, NEW_COUNT, NEWDATE, OLD_COUNT, OLD_DATE, PRCNT_CHANGE)
VALUES
(src.MODEL, src.NEW_COUNT, src.NEWDATE, src.OLD_COUNT, src.OLD_DATE, src.PRCNT_CHANGE);
INSERT INTO STATISTICS(MODEL,NEW_COUNT,NEW_DATE,OLD_COUNT,OLD_DATE,PRNCT_CHANGE)
SELECT MODEL,
( SELECT COUNT(*)
FROM TABLE(USERS)
),
SYSDATE,
NEW_COUNT,
NEW_DATE,
(((NEW_COUNT) - (OLD_COUNT)) / (NEW_COUNT)*100)
FROM SEMANTIC.COUNT_STATISTICS
WHERE MODEL = '&MY_MODEL'
AND trunc(NEW_DATE) = trunc(NEW_DATE -1)
;
I have two tables with identical schema. Let's name them TestTable and TestTableTemp. I need to copy just two columns from TestTableTemp to TestTable without disrupting other data. The rows in TestTable are a subset of those in TestTableTemp. Let's say the columns that I need to copy are named Column1 and Column2 and that they have identical primary keys reference by column primaryKey.
In mysql I believe this could be done as such or something similar:
UPDATE TestTable, TestTableTemp
SET TestTable.Column1 = TestTableTemp.Column1, TestTable.Column2 = TestTableTemp.Column2
WHERE TestTable.primaryKey = TestTableTemp.primaryKey
Sqlite does not allow for multiple tables to be defined on the update statement as can been seen in their reference data here: http://www.sqlite.org/lang_update.html
The best I could come up with is such:
UPDATE TestTable SET
Column1 = (select TestTableTemp.Column1 from TestTableTemp, TestTable where TestTable.primaryKey = TestTableTemp.primaryKey),
Column2 = (select TestTableTemp.Column2 from TestTableTemp, TestTable where TestTable.primaryKey = TestTableTemp.primaryKey)
WHERE EXISTS(select * from TestTableTemp where TestTable.primaryKey = TestTableTemp.primaryKey"
This gives me a syntax error near "." I am guessing this is because I cannot reference TestTable in the scalar expressions.
Can anyone point me in the right direction? Any help is much appreciated.
EDIT:
I cleaned up the second query a bit. It seems to just set the Column1 and Column2 to the first row from that column from TestTableTemp.
Your original query for comparison:
UPDATE TestTable, TestTableTemp
SET TestTable.Column1 = TestTableTemp.Column1
, TestTable.Column2 = TestTableTemp.Column2
WHERE TestTable.primaryKey = TestTableTemp.primaryKey
Here is the working query (I just slightly changed your version):
http://sqlfiddle.com/#!5/f3a19/9
UPDATE TestTable
SET
Column1 = ( SELECT TestTableTemp.Column1
FROM TestTableTemp
WHERE TestTableTemp.primaryKey = TestTable.primaryKey )
,Column2 = ( SELECT TestTableTemp.Column2
FROM TestTableTemp
WHERE TestTableTemp.primaryKey = TestTable.primaryKey )
WHERE EXISTS( SELECT NULL
FROM TestTableTemp
WHERE TestTableTemp.primaryKey = TestTable.primaryKey )
;
I have this table
CREATE TABLE APmeasure
(id_APmeasure INTEGER PRIMARY KEY AUTOINCREMENT
, RSSI TEXT, TimeOfMeasure DATETIME
, BSSID TEXT, id_APm INTEGER NOT NULL
, FOREIGN KEY (id_APm) REFERENCES APTable (id_Ap) ON DELETE CASCADE)
I want to make a query which would give me distinct results of TimeOfMeasure and BSSID, like this:
SELECT DISTINCT TimeOfMeasure, BSSID
FROM APmeasure
WHERE "condition"
But that would retrieve me the other columns on the table, related to the DISTINCT query.
How do I do it?
Perform distinct/grouping operation,
Join to result of distinct/grouping operation...
Something like:
SELECT [whichever columns you want]
FROM APmeasure
JOIN (
SELECT TimeOfMeasure, BSSID
FROM APmeasure
WHERE [condition]
GROUP BY TimeOfMeasure, BSSID
) x
ON x.TimeOfMeasure = APmeasure.TimeOfMeasure
AND x.BSSID = APmeasure.BSSID
[any other joins you need]