I have two tables. Table A and table B. Table A has a column that is a reference to the primary key to table B. I want to run a select query on table A and then populate the column that referrers to B with all of the data in that row of B.
SELECT * from A a LEFT JOIN B b ON a."b_id" = b."id" WHERE ...
That gives a result with each row containing all of the columns of A and all of the columns of B. It is a confusing mess to figure out which column is from which table. I want to be able to do something like.
row.A."column name"
row.B."column name"
I don't want to have to rename every single column using AS. There must be a better way to do this.
Not a 100% sure what your asking but what I think your asking is.
You want a way to have only column B values to show? If so you could do:
SELECT B.*
FROM A
JOIN B
ON A.b_id = B.id
That will only get you the B columns and data, If you want A also maybe do but you want to have it separate from b maybe do:
SELECT B.*,'|' AS ['|'], A.*
FROM A
JOIN B
ON A.b_id = B.id
Hopefully this is helpful, if not to you maybe another reader.
Related
I have 2 database tables. Table A has to fetch some records based on parameter passed there may or may not be an entry in table B with that key.
What I want to do is:
select a.col1,a.col2,a.col3
FROM table WHERE a.id = 123
This would fetch 20 rows. For one of the rows there is an entry in another table B.
select T_level from table b where b.id = 123
only one record appears with right value.
What I want is to get this in a single query. Something like:
select a.col1,a.col2,a.col3,b.T_level
from a,b
where a.id = 123
and a.id = b.id
When I do that, I get 20 rows and the column T_level as '50' for all the rows, whereas it should be '50' for one correct row, for rest it should be null.
I further tried:
select a.col1,a.col2,a.col3,nvl(b.T_level,0) from a,b
but that doesn't fetch the way I expect.
Firstly, please learn to use ansi sql join syntax. The Oracle join syntax you are using hasn't been considered good practice for decades
SQL Join syntax
If you want to get all records from a and any matching records from b then you need to use a LEFT OUTER JOIN
I have a query that is like this:
SELECT * FROM A JOIN B
Table A and B are almost equal, but I use the join to filter on certain rows. Now my result table is having all columns twice, and this is causing referencing trouble where I am using this table. Therefore I would like to only show table A's columns. Is there a more easy way to achieve this than retyping all column names on the spot of *?
If you only want the columns from A, then use:
select A.*
You can add additional columns as you like:
select A.*, B.special_column
I am updating a daily dashboard. Assume everyday I have two tables TODAY and BEFORE_TODAY. What I have been doing daily was something like:
SELECT a, b FROM TODAY
UNION ALL
SELECT a,b FROM BEFORE_TODAY;
TODAY table is generated daily and is appended to all the data before it. Now, I need to generate a new column say c and in order to UNION ALL the two, I need that to be available on BEFORE_TODAY as well.
How can I add a conditional statement to BEFORE_TODAY to check if I have a c column and use that column, else use NULL instead of it.
Something is wrong with your data model. You should be putting the data into separate partitions of the same table. Then you would have no problems. You could just query the master table for the partitions you want. The column would appear in the history, with a NULL value.
That is the right solution. You can create a hacked solution, assuming that your tables have a primary key. For instance, if a, b is unique on each row, you could do:
select t.a, t.b, t.c
from today t
union all
select b.a, b.b,
(select c -- not qualified on purpose
from before_today b2
where b2.a = b.a and b2.b = b.b
) as
from before_today b cross join
(select null as c) c;
If b.c does not exist, then the subquery returns c.c. If it does exist this it returns b2.c from the subquery.
Although by combining dynamic SQL and INFORMATION_SCHEMA, you can write a script to achieve what you told, this doesn't seems to be the right thing to do.
As part of your data model planning, you should add column c to BEFORE_TODAY ahead of time. The newly added column on existing rows will always have NULL value. Then you can add column to TODAY and reference column c as normal.
Questions similar to this one about using DISTINCT values in an INNER JOIN have been asked a few times, but I don't see my (simple) use case.
Problem Description:
I have two tables Table A and Table B. They can be joined via a variable ID. Each ID may appear on multiple rows in both Table A and Table B.
I would like to INNER JOIN Table A and Table B on the distinct values of ID which appear in Table B and select all rows of Table A with a Table A.ID which appears matching some condition in Table B.
What I want:
I want to make sure I get only one copy of each row of Table A with a Table A.ID matching a Table B.ID which satisfies [some condition].
What I would like to do:
SELECT * FROM TABLE A
INNER JOIN (
SELECT DISTINCT ID FROM TABLE B WHERE [some condition]
) ON TABLE A.ID=TABLE B.ID
Additionally:
As a further (really dumb) constraint, I can't say anything about the SQL standard in use, since I'm executing the SQL query through Stata's odbc load command on a database I have no information about beyond the variable names and the fact that "it does accept SQL queries," ( <- this is the extent of the information I have).
If you want all rows in a that match an id in b, then use exists:
select a.*
from a
where exists (select 1 from b where b.id = a.id);
Trying to use join just complicates matters, because it both filters and generates duplicates.
I'm working with three tables, and for simplicity's sake let's call them table A, B, and C. Both tables A and B have a column called id, as well as one other column, Aattribute and Battribute, respectively. Column c also has an id column, and two other columns which hold values for A.id and B.id. Now, in my code, I have easy access to values for both Aattribute and Battribute, and want to delete the row at C, so effectively I want to do something like this:
DELETE FROM C WHERE aid=(SELECT id FROM A WHERE Aattribute='myvalue') AND bid=(SELECT id FROM B WHERE Battribute='myothervalue')
But this obviously doesn't work. Is there any way to make a single complex query, or do I have to run three queries, where I first get the value of A.id using a SELECT with 'myvalue', then the same for B.id, then use those in the final query?
[Edit: it's not letting me comment, so in response to the first comment on this: I tried the above query and it did not work, I figured it just wasn't syntactically correct. Using MS Access, for what it's worth. ]
You must use IN instead of =.
DELETE
FROM C
WHERE aid IN
(SELECT id
FROM A
WHERE Aattribute='myvalue'
)
AND bid IN
(SELECT id
FROM B
WHERE Battribute='myothervalue'
)