I have 2 tables in MS Access and need to query them looking for a value. If the value is in A, then use that. If value is in B, then use that. If the value is in both tables, then use only the value from table A.
How can I make a query to do that?
Thanks!
How about:
SELECT IIF(IsNull(AField),(SELECT AField FROM Table2 WHERE ID=16), AField)
FROM Table1
WHERE ID=16
If you want to do an entire table rather than 1 row :-
select C1, C2 from TableA where C2 is not null
union all
select C1, C2 from TableB where C1 in ( select c1 from TableA where C2 is null )
Related
I have the following scenario.I have 3 tables with the following structure.
TABLE A
-entry_id (PRIMARY KEY, INTEGER)
TABLE B
-entry_id (FOREIGN_KEY -> TABLE A)
-content (TEXT)
TABLE C
-entry_id (FOREIGN_KEY -> TABLE A)
-content (INTEGER)
I want to retrive the content cell value from either table B or table C. The value can be in just one of the table. So it is either table B or C witch have an entry with a given entry_id.
PS. Sorry if duplicate did not manage to find anything to match what i need.
If I correctly understand, you need something like:
select entry_id, content::text from TABLEB where entry_id = ?
union all
select entry_id, content::text from TABLEC where entry_id = ?
union all
select entry_id, content::text from TABLED where entry_id = ?
If it can only exist in one table at a time, use a union
select a1.entry_id, b2.content
from TableA a1
inner join TableB b2
on a1.entry_id = b2.entry_id
union -- This removes any duplicates. Use UNION ALL to show duplicates
select a1.entry_id, c3.content::text
from TableA a1
inner join TableC c3
on a1.entry_id = c3.entry_id
With this sample data...
c1 c2 c3
10 a 10a
11 a **NULL**
12 a **NULL**
13 b 13b
13 b **NULL**
etc..
I want to assign c3 value to rows where it is NULL and c2 value is the same, but do not wish to actually update that value in table, only use it to join to another table while select runs.
I am able to do it using inner select and join, but I want to save as much processing power as possible because amount of data is huge and thought that some use of ISNULL or COALESCE should be able to do it, but I don't have enough experience to figure it on my own yet, or even say if it is possible. What do you think?
select
a.c1,
a.c2,
coalesce( a.c3, b.c3) as c3
from table1 a
left join table1 b
on a.c2 = b.c2
an a.c3 is null
and b.c3 is not null
this will work with the data that you have however if there is more than one row that is not null for c3 for a given c2 it will cause problems
If your DB supports max() over you can also do this
SELECT c1,
c2,
coalesce(c3, MAX(C3) over (partition by c2)) c3
from table1
demo
A sample pseudo code which i often use in my Query.
DECLARE #USER_ID AS VARCHAR(256)
SELECT #USER_ID = 'abc'
select *
from CC
INNER JOIN adm_co_users CR_US WITH(NOLOCK) ON ISNULL(CR_US.original_userID,'') =
(CASE ISNULL(CC.Createdby,'') WHEN '' THEN #USER_ID
ELSE CC.Createdby END )
Below is the structure of table I have: -
Table T1
C1 C2 C3
----------
X P A
X P B
Y Q C
Y Q D
Desired output: -
C1 C2 C3
------------
X P A,B
Y Q C,D
Note: - I know i can do the same with For XML('') with group by on C1 and C2, but the main problem in my case is that the table T1 here must be a physical table object (either permanent or temp or table var or CTE) in DB. But in my case it's a derived table and when i am using the below query it's saying invalid object.
In my case it's not good to replace the derived table with temp# tables or fixed tables or even with CTE or table variable because it will take a great effort.
SELECT
b.C1, b.C2, Stuff((',' + a.C3 from t1 a where a.c1 = b.c1 for XML PATH('')),1,1,'') FROM
T1 b group by b.c1,b.c2
I did not have T1 as fixed table. Please consider it as derived table only.
I need the solution with existing derived table.
Please help.
Below is the query with derived table: -
Please consider this only as a demo query. It's not as simple as given below and a lot of calculations have done to get the derived tables and 4 levels of derived tables have been used.
SELECT C1, C2, Stuff((',' + a.C3 from A B where a.c1 = b.c1 for XML PATH('')),1,1,'')
FROM
(
SELECT C1, C2, C3 FROM T1 WHERE C1 IS NOT NULL--and a lot of calculation also
)A
Please mind that T1 is not just below one step, in my case T1 the actual physical table is 4 level downs by derived tables.
If you can post the query the produces derived table, we can help you work it out, but as of the moment try substituting table1 with the derived query.
;WITH Table1
AS
(
SELECT C1, C2, C3 FROM T1 WHERE C1 IS NOT NULL--and a lot of calculation also
)
SELECT
C1,C2,
STUFF(
(SELECT ',' + C3
FROM Table1
WHERE C1 = a.C1 AND C2 = a.C2
FOR XML PATH (''))
, 1, 1, '') AS NamesList
FROM Table1 AS a
GROUP BY C1,C2
SQLFiddle Demo
I have three tables, A, B, and C. They all hold different data, but have some columns in common.
If A, B, and C all have columns C1 and C2 then how can I look up a specific C2 value using a C1 value that could be in any of the 3 tables?
Basically, I want to do a simple look-up but have it act on the union of the 3 tables - and I'd prefer to not use a view to achieve this.
Note that this is an Ingres Vectorwise database.
You do this by doing a union of the tables in the from clause:
select c2
from ((select c1, c2 from a) union all
(select c1, c2 from b) union all
(select c1, c2 from c)
) t
where c1 = <your value>
I've used union all for performance reasons. If you are concerned about duplicate values, either use union or add a distinct in the select.
This is standard SQL and should work in any database.
I don't know what you mean by " a specific C2 value using a C1 value ",
but, whatever your query would be for the view, repeat that query and union the results,
SELECT *
FROM A
WHERE C2 = ?
UNION ALL
SELECT *
FROM B
WHERE C2 = ?
UNION ALL
SELECT *
FROM C
WHERE C2 = ?
(The view is a standard SQL feature, and will make any query you write easier.)
I have 2 sets of 2 corresponding tables (4 tables total). The two sets only correspond in one column. I want the query to search through that one column in both joined tables, and be able to return the value in the selected column, even if that column doesn't exist in the other table.
Currently, my query looks like:
select z
FROM A1
INNER JOIN A2
ON A1.x=A2.x
WHERE A1.x= '25'
UNION
select z
FROM B1
INNER JOIN B2
ON B1.x=B2.x
WHERE B1.x= '25'
UNION works as long as I am looking for a column which both (joined) tables A and B have in common. I'd like to be able to get values from columns which only exist in A or in B, but not necessarily both of them.
Thanks in advance.
Edit:
Basically, I want two completely separate queries on separate tables, but in one query, with only one select.
Example:
Table A1
x | y
------
1 | a
2 | b
Table A2
x | z
------
1 | c
2 | d
Table B1
x | v
------
3 | e
4 | f
Table B2
x | w
------
3 | g
4 | h
So I want look for a column variable (such as v,w,y, or z), with a specified value of x. e.g. select w where x=4 should give me h; select z where x=2 should give me d.
You must have the same number of columns in each select statement when using UNION. You can add constant values for columns that are missing. You must also have the same data type for each column.
select Column1, null as Column2
from T1
union
select '', Column2
from T2
As per comment by #Adrian, you can of course use null as a constant value. Otherwise you need to pick a constant value of the data type that is used for the column.
select Column1, null as Column2
from T1
union
select null, Column2
from T2
Use the sample data provided in the question:
select A1.x, A2.z as 'y'
from A1
inner join A2
on A1.x=A2.x
where A1.x= 4
union
select B1.x, B2.w as 'y'
from B1
inner join B2
on B1.x=B2.x
where B1.x= 4
Result:
x y
4 h
With a 2 instead of a 4
Result:
x y
2 d
It would be something like that:
select Column1, ColumnThatOnlyExistsInContextA, null as ColumnThatOnlyExistsInContextB
FROM A1
INNER JOIN A2
ON A1.ID=A2.ID
WHERE A1.ID= '25'
UNION
select Column1, null, ColumnThatOnlyExistsInContextB
FROM B1
INNER JOIN B2
ON B1.ID=B2.ID
WHERE B1.ID= '25'
When using UNION, make sure all queries return result sets that have the same number of columns with the same type. If you want to return a column from the second query in a union that the first query doesn't have, you can modify your first query to have a NULL value for that column.
So you basically want to do:
select Column1
FROM A1
INNER JOIN A2
ON A1.ID=A2.ID
WHERE A1.ID= '25'
UNION
select Column2
FROM B1
INNER JOIN B2
ON B1.ID=B2.ID
WHERE B1.ID= '25'
right?
If so, your problem is probably just that Column1 and Column2 are different types. So, do something like
select cast(Column1 as varchar(255))
and
select cast(Column2 as varchar(255))
Should work!
Well, UNION's only requirement is that the number and type of the fields in each result set being UNIONed must match. So, if B has a Column2 and A doesn't, you can select Column1 from the joined As and Column2 from the joined Bs, and provided A.Column1 and B.Column2 are the same type (you can CAST or CONVERT if necessary) the statement will still work. Maybe I'm not understanding the problem, but I think it's pretty easy to solve.