I've a postgres table with data like
Name
Attendance
Jackie
2
Jade
5
Xi
10
Chan
15
In my query I want all present by name, and if name doesn't exist return "null" instead of no row for that particular name
Eg
query where Name in ('Jackie', 'Jade', 'Cha', 'Xi')
Should return
Name
Attendance
Jackie
2
Jade
5
NULL
NULL
Xi
10
To produce the desired rows, you need to join with a table or set of rows which has all those names.
You can do this by inserting the names into a temp table and joining on that, but in Postgres you can turn an array of names into a set of rows using unnest. Then left join with the table to return a row for every value in the array.
select attendances.*
from
unnest(ARRAY['Jackie','Jade','Cha','Xi']) as names(name)
left join attendances on names.name = attendances.name;
Related
I am trying to import specified data using query importrange but at the same time I want to reduce need for additional calculation columns and by using concat or something similar to add 2 columns together with a space in between ie. first name 'bob' last name 'smith' returns 'bob smith' in 1 column
=QUERY({IMPORTRANGE("https://docs.google.com/spreadsheets/d/1oaZP3-p1cI4d1QyLQ2qM5sMwnVGz8S0bhe29W4QqH6g/edit#gid=1908577977","Sheet7!A2:c"),"select Col1&" "&Col2,Col3",0})
I've tried the above but it returns formula parse error
https://docs.google.com/spreadsheets/d/1oaZP3-p1cI4d1QyLQ2qM5sMwnVGz8S0bhe29W4QqH6g/edit?usp=sharing
in post-IMPORTRANGE you can join two columns only like this:
=FLATTEN(QUERY(TRANSPOSE(QUERY(
IMPORTRANGE("13Ptmj3sejlOADvwhgfBPxRy_H-RGCxLX4r2jecbceIE", "Sheet7!A2:C"),
"select Col1,Col2", )),,9^9))
so for 3 columns:
={FLATTEN(QUERY(TRANSPOSE(QUERY(
IMPORTRANGE("13Ptmj3sejlOADvwhgfBPxRy_H-RGCxLX4r2jecbceIE", "Sheet7!A2:C"),
"select Col1,Col2", )),,9^9)),
IMPORTRANGE("13Ptmj3sejlOADvwhgfBPxRy_H-RGCxLX4r2jecbceIE", "Sheet7!C2:C")}
Our system uses postgres for its database.
We have queries that can select rows from a database table where an array field in the table contains a specific value, e.g.:
Find which employee manages the employee with ID 123.
staff_managed_ids is a postgres array field containing an array of the employees that THIS employee manages.
This query works as expected:
select *
from employees
where 123=any(staff_managed_ids)
We now need to query where an array field contains a postgres NULL. We tried the following query, but it doesn't work:
select *
from employees
where NULL=any(staff_managed_ids)
We know the staff_managed_ids array field contains NULLs from other queries.
Are we using NULL wrongly?
NULL can not be compared using =. The only operators that work with that are IS NULL and IS NOT NULL.
To check for nulls, you need to unnest the elements:
select e.*
from employees e
where exists (select *
from unnest(e.staff_managed_ids) as x(staff_id)
where x.staff_id is null);
if all your id values are positive, you could write something like this:
select *
from employees
where (-1 < all(staff_managed_ids)) is null;
how this works is that -1 should be less than all values, however comparison with null will make the whole array comparison expression null.
I have two columns of dates and I want to run a query that returns TRUE if there is a date in existence in the first column and in existence in the second column.
I know how to do it when I'm looking for a match (if the data entry in column A is the SAME as the entry in column B), but I don't know know how to find if data entry in column A and B are in existence.
Does anyone know how to do this? Thanks!
If data in a column is present, it IS NOT NULL. You can query for that on both columns, with and AND clause to get your result:
SELECT (date1 IS NOT NULL AND date2 IS NOT NULL) AS both_dates
FROM mytable;
So, rephrasing:
For any two entries in table x with date columns a and b, is there some pair of rows x1 and x2 where x1.a = x2.b?
If that's what you're trying to do, you want a self-join, e.g, presuming the presence of a single key column named id:
SELECT x1.id, x2.id, x1.a AS x1_a_x2_b
FROM mytable x1
INNER JOIN mytable x2 ON (x1.a = x2.b);
Is there any other way for returning rows for the same id by joining two tables and return the row if any of the columns value for the same id is different.
Select Table1.No,Table2.No,Table1.Name,Table2.Name,Table1.ID,Table2.ID,Table1.ID_N,Table2.ID_N
From MyFirstTable Table1
JOIN MySecondTable Table2
ON Table1.No=Table2.No where Table1.ID!=Table2.ID or Table1.ID_N != Table2.ID_N
In the example above , I have only two columns I need to check but in my real case there are at least 20 .
Is there any other statment I can use instead of enumerating each column in the where codition?
...WHERE BINARY_CHECKSUM(Table1.*) <> BINARY_CHECKSUM(Table2.*)
or
...WHERE BINARY_CHECKSUM(Table1.Field1, Table1.Field2, ...) <> BINARY_CHECKSUM(Table2..Field1, Table2.Field2, ...)
*this assumes you have no blob fields in your tables
http://technet.microsoft.com/en-us/library/ms173784.aspx
If No is a PK
Select Table1.No,Table1.Name,Table1.ID,Table1.ID_N
From MyFirstTable Table1
except
Select Table1.No,Table1.Name,Table1.ID,Table1.ID_N
From MySecondTable Table1
I want to get grouped data from a table in sqlite. For example, the table is like below:
Name Group Price
a 1 10
b 1 9
c 1 10
d 2 11
e 2 10
f 3 12
g 3 10
h 1 11
Now I want get all data grouped by the Group column, each group in one array, namely
array1 = {{a,1,10},{b,1,9},{c,1,10},{h,1,11}};
array2 = {{d,2,11},{e,2,10}};
array3 = {{f,3,12},{g,3,10}}.
Because i need these 2 dimension arrays to populate the grouped table view. the sql statement maybe NSString *sql = #"SELECT * FROM table GROUP BY Group"; But I wonder how to get the data from the resultset. I am using the FMDB.
Any help is appreciated.
Get the data from sql with a normal SELECT statement, ordered by group and name:
SELECT * FROM table ORDER BY group, name;
Then in code, build your arrays, switching to fill the next array when the group id changes.
Let me clear about GroupBy. You can group data but that time its require group function on other columns.
e.g. Table has list of students in which there are gender group mean Male & Female group so we can group this table by Gender which will return two set . Now we need to perform some operation on result column.
e.g. Maximum marks or Average marks of each group
In your case you want to group but what kind of operation you require on price column ?.
e.g. below query will return group with max price.
SELECT Group,MAX(Price) AS MaxPriceByEachGroup FROM TABLE GROUP BY(group)