Is it possible in any way (without scripting) to aggregate columns which are stored in a table cell.
Basically what i am trying to achieve here is that if i have the following table
Table 1
KEYNAME | COLUMN_NAME
COUNT_USER | USER_ID
SUM_HOURS | HOURS_WATCHED
Can i do something like
select SUM((select column_name from TABLE1 where KEYNAME = "SUM_HOURS")) FROM MAIN_TABLE
I have the option to script in python via which i know how to achieve this. But i am curious to know if this is possible in any version of SQL or not
Please let me know if the information is insufficient.
No, you cannot use a column name that comes from the result of another query.
You would need to do this in your own code, sending the result to Amazon Redshift as a complete query. (That is, run one query to obtain the column names, then run a second query with those column names inserted.)
Related
So the problem is that I have three huge table with same structure, and I need to show the results of one of them depending on result from another query.
So my order table looks like that:
code order
A 0
B 2
C 1
And I need to retrieve data from t_results
My approach (which is working) looks like this:
select *
from t_results_a
where 'A' in (
select code
from t_order
where order = 0
)
UNION ALL
select *
from t_results_b
where 'B' in (
select code
from t_order
where order = 0
)
UNION ALL
select *
from t_results_c
where 'C' in (
select code
from t_order
where order = 0
)
Is there anyway to not scan all three tables, as I am working with Athena so I can't program?
I presume that changing your database schema is not an option.
If it were, you could use one database table and add a CODE column whose value would be either A, B or C.
Basically the result of the SQL query on your ORDER table determines which other database table you need to query. For example, if CODE in table ORDER is A, then you have to query table T_RESULTS_A.
You wrote in your question
I am working with Athena so I can't program
I see that there is both an ODBC driver and a JDBC driver for Athena, so you can program with either .NET or Java. So you could write code that queries the ORDER table and use the result of that query to build another query string to query just the relevant table.
Another thought I had was dynamic SQL. Oracle database supports it. I can create a string containing variables where one variable is the database table name and have Oracle interpret the string as SQL and execute it. I briefly searched the Internet to see whether Athena supports this (as I have no experience with Athena) but found nothing - which doesn't mean to say that it does not exist.
My overall goal is to create new tables by selecting columns in existing tables with certain patterns/tags in their column names. This is in SQL Server.
For example, I have a common need to get all contact information out of a company table, and into its own contact table.
I haven't been able to find a programmatic approach in SQL to express excluding columns from a SELECT statement based on string.
When looking to options like the COL_NAME function, those require an ID arg, which kills that option for me.
Wishing there was something built in that could work like the following:
SELECT *
FROM TABLE
WHERE COL_NAME() LIKE 'FLAG%'
Any ideas? Open to anything! Thanks!!
One trick could be to firstly using the following code to get the column names you desire:
select * from information_schema.columns
where table_name='tbl' and column_name like 'FLAG%'
Then concatenate them into a comma-delimited string and finally create a dynamic sql query using the created string as the column names.
I need dynamically obtain table name from system table and perform a select query on this table example:
SELECT "schema"+'.'+"table" FROM SVV_TABLE_INFO WHERE "table" LIKE '%blabla%'
it returns my_schema.the_main_blabla_table
And after I get this table name I need to perform :
SELECT * FROM my_schema.the_main_blabla_table LIMIT 100
Is it possible to in a single query?
If you are talking about select subquery after "from" i can say that you can do this.
You will get something like this:
SELECT * FROM
(
SELECT "schema"+'.'+"table" FROM SVV_TABLE_INFO WHERE "table" LIKE '%blabla%'
)
LIMIT 100
Unfortunately, i can't test it on yor data, but i very interested in result because i have never done something like this. If i get your question incorrect, tell me pls.
Amazon Redshift does not support the ability to take the output of a query and use it as part of another query.
Your application will need to query Redshift to obtain the relevant table name(s), then make another call to Redshift to query that table.
Hello StackOverflow community,
Could you please tell me can I get information about column names of a table in 1 row using Firebird? [*]
What I'd like to achieve is the following using Postgres:
SELECT * FROM table_name LIMIT 0;
Above statement would return 0 rows, but will contain the header
id | data
---+-------
(0 rows)
[*] I need a similar way (taken from example above) in Firebird to obtain information about columns, since I'm using it external tool, so I need to provide a dynamically built schema for dynamic queries. This implies, that I'm not looking for a solution using system tables like rdb$relation_fields.
Adding WHERE condition with dummy value does not apply in my case. I'm looking for something like SELECT FIRST 0 .... Does it even exist?
edited: Yes, it does. Interactive Firebird Client doesn't show up anything, but it does indeed return the "header". This may be confusing for some of us that use psql console which yields 0 rows, but does contain the "header" itself.
Firebird supports limiting the result set - but the syntax is a bit different:
SELECT FIRST 0 *
FROM table_name;
This is part of the Firebird FAQ: http://www.firebirdfaq.org/faq111/
What about this?
select * from (
[any query here]
) where 1=0
I'm using Oracle DB and I would like to write a SQL query that I could then call with JDBC. I'm not very familiar with SQL so if someone can help me, that could be great ! Here is the problem. I have a table MY_TABLE wich contains a list of another tables, and I would like to keep only the nonempty tables and those that their names start by a particular string.
The query I wrote is the following :
select TABLE_NAME
from MY_TABLE
where TABLE_NAME like '%myString%'
and (select count(*) from TABLE_NAME where rownum=1)<>0
order by TABLE_NAME;`
The problem comes from the second SELECT, but I don't know how can I do to use the TABLE_NAME value.
Does someone have an idea ?
Thanks.
[Added from comments]
Actually, I need to test the V$ views contained in the ALL_CATALOG table. But if I can find another table where all these views are contained too and with a NUM_ROWS column too, it would be perfect !
Standard versions of SQL do not allow you to replace 'structural elements' of the query, such as table name or column name, with variable values or place-holders.
There are a few ways to approach this.
Generate a separate SQL statement for each table name listed in MY_TABLE, and execute each in turn. Brute force, but effective.
Interrogate the system catalog directly.
Investigate whether there are JDBC metadata operations that allow you to find out about the number of rows in a table without being tied to the system catalog of the specific DBMS you are using.
Can you use oracle view USER_TABLES? then query will be much easier
select TABLE_NAME
from USER_TABLES
where TABLE_NAME like '%myString%'
and Num_ROWS > 0
order by TABLE_NAME;`