I have a table that has two columns.
id|custom_id
1 |9123
2 |null
null|null
I want to output it like:
id
1
2
9123
I tried SELECT id FROM table UNION SELECT custom_id FROM table and it works fine, but the output contains an empty line which is because of null values. If use WHERE id IS NOT null as condition on each SELECT query it works. Is there any other way to achieve the desired output?
This is not more efficient than using a WHERE column is not null and it rejects duplicates from each column:
SELECT id FROM table group by id having max(id) = id
UNION ALL
SELECT custom_id FROM table group by custom_id having max(custom_id) = custom_id
Related
I have two tables whose relevant columns look more or less like the following:
table1.id:
zIXuJeY-qH
zJrcULGLXK
zXyIgnlylb
zZ7MYDGDAV
zbCFI4wKpe
ziGeauO-0O
zmzWbaGSb7
table2.id
zIXuJeY-qH
zIXuJeY-qH
zIXuJeY-qH
zIXuJeY-qH
zJrcULGLXK
zJrcULGLXK
in which table1.id is a primary key and table2.id is not a primary key. I'm trying to grab all the IDs from table 1 that are not in table 2, but am having trouble. If, for instance, I select a count of all the values that are in table two, I get:
>SELECT COUNT(id) FROM table1 WHERE id IN (SELECT id FROM table2);
>2
But if I try to find the IDs not in table2, I get 0:
>SELECT COUNT(id) FROM table1 WHERE id NOT IN (SELECT id FROM table2);
>
There are 503 unique IDs in table1 and only 163 in table2. What am I doing wrong?
I suppose there can be nulls in table2.id?
NOT IN ( ..., null, ...)
does never result in true unfortunately (because - so the argumentation - null is the unknown value, and we cannot guarantee that the unknown value is not the value you are looking for obviously). A bad trap.
Try
SELECT COUNT(id) FROM table1 WHERE id NOT IN (SELECT id FROM table2 where id is not null);
or an EXISTS clause instead.
I have two tables, one with objects, one with properties of the objects. Both tables have a personal ID and a date as "key", but since multiple orders of objects can be done by one person on a single day, it doesn't match well. I do know however, that the entries are entered in the same order in both tables, so it is possible to join on the order, if the personID and date are the same.
This is what I want to accomplish:
Table 1:
PersonID Date Object
1 20-08-2013 A
2 13-11-2013 B
2 13-11-2013 C
2 13-11-2013 D
3 21-11-2013 E
Table 2:
PersonID Date Property
4 05-05-2013 $
1 20-08-2013 ^
2 13-11-2013 /
2 13-11-2013 *
2 13-11-2013 +
3 21-11-2013 &
Result:
PersonID Date Object Property
4 05-05-2013 $
1 20-08-2013 A ^
2 13-11-2013 B /
2 13-11-2013 C *
2 13-11-2013 D +
3 21-11-2013 E &
So what I want to do, is join the two tables and "zip" the group of entries that have the same (PersonID,Date) "key".
Something called "Slick" seems to have this (see here), but I'd like to do it in SQLite.
Any advice would be amazing!
You are on the right track. Why not just do a LEFT JOIN between the tables like
select t2.PersonID,
t2.Date,
t1.Object,
t2.Property
from table2 t2
left join table1 t1 on t2.PersonID = t1.PersonID
order by t2.PersonID
Use a additional column to make every key unique in both tables. For example in SQLite you could use RowIDs to keep track of the order of insertion. To store this additional column in the database itself might be useful for other queries as well, but you do not have to store this.
First add the column ID to both tables, the DDL queries should now look like this: (make sure you do not add the primary key constraint until both tables are filled.
CREATE TABLE table1 (
ID,
PersonID,
Date,
Object
);
CREATE TABLE table2 (
ID,
PersonID,
Date,
Property
);
Now populate the ID column. You can adjust the ID to your liking. Make sure you do this for table2 as well:
UPDATE table1
SET ID =(
SELECT table1.PersonID || '-' || table1.Date || '-' || count( * )
FROM table1 tB
WHERE table1.RowID >= tB.RowID
AND
table1.PersonID == tB.PersonID
AND
table1.Date == tB.Date
);
Now you can join them:
SELECT t2.PersonID,
t2.Date,
t1.Object,
t2.Property
FROM table2 t2
LEFT JOIN table1 t1
ON t2.ID = t1.ID;
I would like to determine particular IDs that are not present in a table.
For example, I have the IDs 1, 2 and 3 and want to know if they exist in the table.
Essentially this would boil down to:
SELECT id FROM (
SELECT 1 AS id
UNION
SELECT 2 AS id
UNION
SELECT 3 AS id
)
WHERE
NOT EXISTS (SELECT * FROM table WHERE table.id = id)
Suppose table had the IDs 1 and 4, then this would yield 2 and 3.
Are there more elegant / concise / faster ways to get those IDs in SQLite ?
The compound SELECT operator EXCEPT allows you to do something similar to NOT EXISTS:
SELECT 1 AS id UNION ALL
SELECT 2 UNION ALL
SELECT 3
EXCEPT
SELECT id FROM MyTable
Beginning with SQLite 3.8.3, you can use VALUES everywhere you could use SELECT, but this is just a different syntax:
VALUES (1),
(2),
(3)
EXCEPT
SELECT id FROM MyTable
I'm adding an 'index' column to a table in SQLite3 to allow the users to easily reorder the data, by renaming the old database and creating a new one in its place with the extra columns.
The problem I have is that I need to give each row a unique number in the 'index' column when I INSERT...SELECT the old values.
A search I did turned up a useful term in Oracle called ROWNUM, but SQLite3 doesn't have that. Is there something equivalent in SQLite?
You can use one of the special row names ROWID, OID or _ROWID_ to get the rowid of a column. See http://www.sqlite.org/lang_createtable.html#rowid for further details (and that the rows can be hidden by normal columns called ROWID and so on).
Many people here seems to mix up ROWNUM with ROWID. They are not the same concept and Oracle has both.
ROWID is a unique ID of a database ROW. It's almost invariant (changed during import/export but it is the same across different SQL queries).
ROWNUM is a calculated field corresponding to the row number in the query result. It's always 1 for the first row, 2 for the second, and so on. It is absolutely not linked to any table row and the same table row could have very different rownums depending of how it is queried.
Sqlite has a ROWID but no ROWNUM. The only equivalent I found is ROW_NUMBER() function (see http://www.sqlitetutorial.net/sqlite-window-functions/sqlite-row_number/).
You can achieve what you want with a query like this:
insert into new
select *, row_number() over ()
from old;
No SQLite doesn't have a direct equivalent to Oracle's ROWNUM.
If I understand your requirement correctly, you should be able to add a numbered column based on ordering of the old table this way:
create table old (col1, col2);
insert into old values
('d', 3),
('s', 3),
('d', 1),
('w', 45),
('b', 5465),
('w', 3),
('b', 23);
create table new (colPK INTEGER PRIMARY KEY AUTOINCREMENT, col1, col2);
insert into new select NULL, col1, col2 from old order by col1, col2;
The new table contains:
.headers on
.mode column
select * from new;
colPK col1 col2
---------- ---------- ----------
1 b 23
2 b 5465
3 d 1
4 d 3
5 s 3
6 w 3
7 w 45
The AUTOINCREMENT does what its name suggests: each additional row has the previous' value incremented by 1.
I believe you want to use the constrain LIMIT in SQLite.
SELECT * FROM TABLE can return thousands of records.
However, you can constrain this by adding the LIMIT keyword.
SELECT * FROM TABLE LIMIT 5;
Will return the first 5 records from the table returned in you query - if available
use this code For create Row_num 0....count_row
SELECT (SELECT COUNT(*)
FROM main AS t2
WHERE t2.col1 < t1.col1) + (SELECT COUNT(*)
FROM main AS t3
WHERE t3.col1 = t1.col1 AND t3.col1 < t1.col1) AS rowNum, * FROM Table_name t1 WHERE rowNum=0 ORDER BY t1.col1 ASC
I'd like to do something like this:
Suppose I have two tables, myTable1 and myTable2. Suppose both of these tables have columns myColumn1 and myColumn2.
update
myTable1
set
myTable1.myFlagColumn = 1
where
myTable1.myColumn1, myTable1.myColumn2
in
(select myTable2.myColumn1, myTable2.myColumn2 from myTable2)
Essentially, I want to change a value in myTable1 if there are any rows where the two columns in myTable1 and myTable2 match.
Is this possible?
Yes, but you will use an EXISTS clause:
update
myTable1
set
myTable1.myFlagColumn = 1
where
EXISTS
(select * FROM myTable2 WHERE myTable2.myColumn1 = myTable1.myColumn1
AND myTable2.myColumn2 = myTable1.myColumn2)