Using UNION ALL with Queries with different number of column returns the following error sqlite3.OperationalError: SELECTs to the left and right of UNION ALL do not have the same number of result columns.
I tried
this answer but I think that is now outdated and does not work. I tried to find something in the documentation but I couldn't find it.
Both UNION and UNION ALL do not work.
This answer is a bit complex for me to understand.
What would be the workaround to achieve this? A Column with Null - how do I do that ?
Update:
Also, I don't know the no. or name of tables as in my program I allow the user to create and manipulate data.
To find out the queries in the database, I Use:
SELECT name FROM sqlite_master WHERE type='table';
and to find out the columns I use this:
[i[0] for i in cursor.description]
Simple, the column size and type for each side of a union must be identical.
You can make them identical by casting columns to the correct type, or setting missing columns to NULL.
I think you just need to compensate for the missing columns with adding 'empty' columns.
CREATE TABLE test_table1(k INTEGER, v INTEGER);
CREATE TABLE test_table2(k INTEGER);
INSERT INTO test_table1(k,v) VALUES(4, 5);
INSERT INTO test_table2(k) VALUES(4);
SELECT * FROM test_table1 UNION ALL SELECT *,'N/A' FROM test_table2;
4|5
4|N/A
Here I've added another pseudo-column with 'N/A', so the test_table2 has two columns before the UNION ALL happens.
I have a table where rows appear to be "duplicates" but they are actually not (they have different date).
Suppose each record has a column A that is supposed to be unique. However due to this column A could or could not appear again later with updated information (with column A unchanged), it is no longer unique even when it should be.
Therefore I want the table with latest information only. Currently this table contains 500k entries, however the "true" number of unique entries is less than half of it.
I have tried
SELECT *
FROM TABLE
WHERE A = A
AND Date = (SELECT MAX(Date) from TABLE)
ORDER BY DATE
However this only returns 2 results. How do I achieve that?
The subquery on the date is the correct idea, but you must include the column A in the subquery and relate it back to the main table. I prefer to use explicit joins rather than embedding the subquery in the WHERE statement. This is usually more efficient anyway.
SELECT TABLE.*
FROM TABLE INNER JOIN
(SELECT A, MAX(Date) AS MaxDate FROM TABLE GROUP BY A) AS latest
ON TABLE.A = latest.A AND TABLE.date = latest.MaxDate
ORDER BY A, date
Or even better, I prefer CTE (Common Table Expression) syntax, since it makes the individual queries easier to read:
WITH latest AS (
SELECT A, MAX(Date) AS MaxDate
FROM TABLE
GROUP BY A
)
SELECT TABLE.*
FROM TABLE INNER JOIN latest
ON TABLE.A = latest.A AND TABLE.date = latest.MaxDate
ORDER BY TABLE.A, TABLE.date
Comparison to other answer
The answer by MikeT relies on a non-standard feature of sqlite. That is okay of itself as long as you are aware that the solution is not compatible with other databases engines/servers and SQL dialects.
The next possible gotcha really relies on your actual data and table schema (neither of which you shared in the question details). If your data allows multiple rows with the same date for the a single A column value, then the conditions in your question are not enough to definitively remove all duplicates. You would need to identify another column by which to resolve any remaining duplicates, but once again your question did not do that.
However, in testing, I found that my solution allows unresolved duplicates to remain in the results. MikeT's solution eliminate all duplicates, but it does so by arbitrarily excluding one of those duplicates. There are ways to fix either solution to definitely select which duplicate to keep, but I will not even attempt that unless you post actual data and the table schema so that my answer is not just mere guessing. I'm glad that my answer was useful thus far, but you need to understand your data better (than reveal in the question) to ensure what solution is actually best.
Bonus
Against my better judgement to just keep expanding on answers... since you should really research this separately... here's an example of how you would continue joining this with other queries...
WITH latest AS (
SELECT A, MAX(Date) AS MaxDate
FROM TABLE
GROUP BY A
),
firstResults AS (
SELECT TABLE.*
FROM TABLE INNER JOIN latest
ON TABLE.A = latest.A AND TABLE.date = latest.MaxDate
ORDER BY TABLE.A, TABLE.date
)
SELECT otherTable.*
FROM firstResults JOIN otherTable
ON firstResults.A = otherTable.A
WHERE somecondition = 'foobar'
Another approach if you're using a somewhat recent version of sqlite (3.25 or newer), using the row_number() window function to rank groups of the same a value by date and picking the first one:
WITH cte AS
(SELECT a, date, row_number() OVER (PARTITION BY a ORDER BY date DESC) AS rn
FROM yourtable)
SELECT a, date
FROM cte
WHERE rn = 1;
One important thing to note since I noticed you mentioning another answer was slow is that an index on mytable(a, date DESC) will be needed for this query for best results, and an index on mytable(a, date) will speed up the other answers given.
I believe, if I understand what you have written, that you could use :-
SELECT a,max(date), other FROM mytable GROUP BY a ORDER BY date;
note that the other column represents other columns (if present)
However, the other column will be an arbritary value (from one of the grouped columns) which may well be the required value (in the example it is).
As per :-
Each expression in the result-set is then evaluated once for each
group of rows. If the expression is an aggregate expression, it is
evaluated across all rows in the group. Otherwise, it is evaluated
against a single arbitrarily chosen row from within the group. If
there is more than one non-aggregate expression in the result-set,
then all such expressions are evaluated for the same row.
SQL As Understood By SQLite - SELECT
More correctly, to eliminate an arbritary value(sic) for the other column, you could use :-
SELECT
a /* will always be the same and isn't arbritary */,
max(date) /* will be the maximum data */ AS date,
(SELECT other FROM mytable WHERE a = m.a AND date = m.date) AS other
FROM mytable AS m /* AS m allows the outer query to be distinguished from the inner query */
GROUP BY a /* this effectivel removes duplicates on the a column */
ORDER BY date
;
The example below appears to produce the same result.
Example :-
Using the following to populate the table with some generated testing data :-
CREATE TABLE IF NOT EXISTS mytable (a TEXT, date TEXT, other);
WITH cte(count,a,date,other) AS
(
SELECT 1,1,date('now','+'||(random() % 30)||' days'),'other1'
UNION ALL SELECT count+1,abs(random()) % 20,date('now','+'||(abs(random()) % 30)||' days'), 'other'||(count+1) FROM cte LIMIT 100
INSERT INTO mytable (a,date,other) SELECT a,date,other FROM cte
;
SELECT * FROM mytable ORDER BY DATE DESC;
in this case :-
Highlighted rows being those required to be extracted.
Then after the above has been run the following is run
SELECT * FROM mytable WHERE a = a AND date = (SELECT MAX(date) FROM mytable);
SELECT * FROM mytable WHERE /*a = a AND*/ date = (SELECT MAX(date) FROM mytable);
/* Will only select 1 row per unique value of a BUT other will be an arbritary value not necessairlly the latest */
SELECT a,max(date), other FROM mytable GROUP BY a /* group by effectively display unique */;
SELECT
a /* will always be the same and isn't arbritary */,
max(date) /* will be the maximum data */ AS date,
(SELECT other FROM mytable WHERE a = m.a AND date = m.date) AS other
FROM mytable AS m
GROUP BY a
;
The first two results show that a = a does nothing as it will always be true.
The thrid query produces (unordered) :-
Note ticks assigned by checking the value of other from the previous result.
In this case this shorter query works OK even though values of other are arbritary values (they aren't really as it depends upon how the query planner plasn the query).
The fourth, the more correct, produces the same results :-
Result 2 (your orignal query) and 3 (original without a = a) produce :-
and :-
I have this sqlite database:
And I need to get the set from AssignmentMetric for a certain Athlete_id AND for Assignments which include a skill with Value X.
I've looked all over JOIN, LEFT JOIN but cannot find any examples that seems to match exactly this. I can query to get Assignment metrics for a particular Athlete ID And Assignment ID, but I am trying to narrow the Assignments to ones that are for a specific skill "of X value". How do I "reach through" the Assignment table to grab the value from the Skill table?
You could do:
SELECT ...
FROM
AssignmentMetric
INNER JOIN Assignment
ON AssignmentMetric.Assignment_id =
Assignment.Assignment_id
INNER JOIN
Skill
ON Skill.Skill_id = Assignment.Skill_id
WHERE ...
In the WHERE you can refer to the colums of the tables using the tablename.columnname notation.
Im working with the oracle pdf's to learn pl/sql.
There is an exercise where i have to create a new table with data out
of two other tables already existing. I thought this would do the trick:
CREATE TABLE new_depts
AS SELECT d.department_id, d.department_name, sum(e.salary) dept_sal
FROM employees e, departments d
WHERE e.department_id = d.department_id;
But this raises the following error:
SQL-Fehler: ORA-00937: not a single-group group function
00937. 00000 - "not a single-group group function"
I cant find something usefull about this error. From what i know yet
about SQL my code should work fine!
Am i wrong?
Try adding group by clause :
CREATE TABLE new_depts
AS SELECT d.department_id, d.department_name, sum(e.salary) dept_sal
FROM employees e, departments d
WHERE e.department_id = d.department_id
group by d.department_id,d.department_name
Update 1
You need to use group by clause in your select query because you are using aggregate function: sum(e.salary). If you are using aggregate function then you need to have group by clause. Please see here for more information about group by clause.
The main concept to understanding why aggregate functions or columns that are specified in the GROUP BY clause cannot be mixed with other non aggregate expressions in the select list is the level of detail of the value they produce. The select list of the SELECT statement can include only expressions that produce values that are on the same level of detail as others in that select list.
Example 1: incorrect
SELECT avg(col1) --> level of detail of the value is aggregated
,col2 --> level of detail of the value is only for one row
FROM table_a;
Example 2: correct
SELECT avg(col1) --> level of detail of the value is aggregated
,col2 --> level of detail of the value is aggregated
FROM table_a
GROUP BY col2;
By including a column in the GROUP BY clause you aggregate the specified column and change its level of detail from single row to aggregate.
I have two tables, one contains a list of items which is called watch_list with some important attributes and the other is just a list of prices which is called price_history. What I would like to do is group together 10 of the lowest prices into a single column with a group_concat operation and then create a row with item attributes from watch_list along with the 10 lowest prices for each item in watch_list. First I tried joins but then I realized that the operations where happening in the wrong order so there was no way I could get the desired result with a join operation. Then I tried the obvious thing and just queried the price_history for every row in the watch_list and just glued everything together in the host environment which worked but seemed very inefficient. Now I have the following query which looks like it should work but it's not giving me the results that I want. I would like to know what is wrong with the following statement:
select w.asin,w.title,
(select group_concat(lowest_used_price) from price_history as p
where p.asin=w.asin limit 10)
as lowest_used
from watch_list as w
Basically I want the limit operation to happen before group_concat does anything but I can't think of a sql statement that will do that.
Figured it out, as somebody once said "All problems in computer science can be solved by another level of indirection." and in this case an extra select subquery did the trick:
select w.asin,w.title,
(select group_concat(lowest_used_price)
from (select lowest_used_price from price_history as p
where p.asin=w.asin limit 10)) as lowest_used
from watch_list as w