I'd like to add an extra column to an Arel select result, where the value in the column is the same on every row, so that I can add extra information about the context of the query to a Rails ActiveRecord object.
So, how would I generate this SQL using Arel?
select date('2013-12-25') as foo
It should result in a result with a single column and a single row which contains a date value. I've used MySQL syntax here, but I'd like it to generate correct SQL for whichever backend is being used.
Looks like the answer is:
include Arel
select = SelectManager.new(Table.engine)
select.project(Nodes::NamedFunction.new('date', ['2013-12-25']).as('foo'))
select.to_sql
Related
I want to return arrays with data from the entire row (so all columns), not just a single column. I can do this with a raw sql statement in Postgresql,
SELECT
array_agg(users.*)
FROM users
WHERE
l_name LIKE 'Br%'
GROUP BY f_name;
but when I try to do it with SqlAlchemy, I'm getting
sqlalchemy.exc.ProgrammingError: (psycopg2.ProgrammingError) can't adapt type 'InstrumentedAttribute'
For example, when I execute this query, it works fine
query: Query[User] = session.query(array_agg(self.user.f_name))
But with this I get arrays of rows with only one column value in them (in this example, the first name of a user) whereas I want the entire row (all columns for a user).
I've tried explicitly listing multiple columns, but to no avail. For example I've tried this:
query: Query[User] = session.query(array_agg((self.user.f_name, self.user.l_name))))
But it doesn't work. I get the above error message.
You could use Python feature unpack for create
example = [func.array_agg(column) for column in self.example.__table__.columns]
query = self.dbsession.query(*attach)
And after join results
I'm trying to select NULL as a column in my query using JOOQ, so basically something like this:
SELECT name, NULL as 'someColumn' FROM someTable;
I need to do this, because the result needs to include someColumn (as part of a data standard), but we do not have this information in our database. This works fine in plain SQL, but I'm struggling to reproduce this using JOOQ.
Does anyone know how to do this in a query of this form?
context.select(
SOMETABLE.NAME,
... // Other columns here
DSL.NULL.as("someColumn") // <-- This doesn't exist
)
You can use an inline value
DSL.inline(null)
Depending on your database dialect or query usage, you may need to add a data type to that value, e.g.
DSL.inline(null, SQLDataType.VARCHAR)
I've created a MySQL sproc which returns 3 separate result sets. I'm implementing the npm mysql package downstream to exec the sproc and get a result structured in json with the 3 result sets. I need the ability to filter the json result sets that are returned based on some type of indicator in each result set. For example, if I wanted to get the result set from the json response which deals specifically with Suppliers then I could use some type of js filter similar to this:
var supplierResultSet = mySqlJsonResults.filter(x => x.ResultType === 'SupplierResults');
I think SQL Server provides the ability to include a hard-coded column value in a SQL result set like this:
select
'SupplierResults',
*
from
supplier
However, this approach appears to be invalid in MySQL b/c MySQL Workbench is telling me that the sproc syntax is invalid and won't let me save the changes. Do you know if something like what I'm trying to achieve is possible in MySQL and if not then can you recommend alternative approaches that would help me achieve my ultimate goal of including some type of fixed indicator in each result set to provide a handle for downstream filtering of the json response?
If I followed you correctly, you just need to prefix * with the table name or alias:
select 'SupplierResults' hardcoded, s.* from supplier s
As far as I know, this is the SQL Standard. select * is valid only when no other expression is added in the selec clause; SQL Server is lax about this, but most other databases follow the standard.
It is also a good idea to assign a name to the column that contains the hardcoded value (I named it hardcoded in the above query).
In MySQL you can simply put the * first:
SELECT *, 'SupplierResults'
FROM supplier
Demo on dbfiddle
To be more specific, in your case, in your query you would need to do this
select
'SupplierResults',
supplier.* -- <-- this
from
supplier
Try this
create table a (f1 int);
insert into a values (1);
select 'xxx', f1, a.* from a;
Basically, if there are other fields in select, prefix '*' with table name or alias
I'm working of generating sql request by parsing Excel-like formulas.
So for a given formula, I get this request :
SELECT IF(COL1='Y', SUM(EXPR),NULL)
FROM Table
I don't get the results I want. If I manually rewrite the request like this it works :
SELECT SUM(IF(COL1='Y', EXPR, NULL))
FROM Table
Also, the first request produces the right value if I add a GROUP BY statement, for COL1='Y' row :
SELECT IF(COL1='Y', SUM(EXPR),NULL)
FROM Table
GROUP BY COL1
Is there a way to keep the first syntax IF(COND, SUM(EXPR), NULL) and slightly edit it to make it works without a GROUP BY statement ?
You have to use GROUP BY since you are using SUM - otherwise SQL engine is not able to tell how do you want to summarize the column.
Alternatively you could summarize this column only:
SELECT SUM(EXPR)
FROM Table
WHERE COL1='Y'
But then you would have to run separate query for each such column, read: not recommended for performance reasons.
I want to produce sql like:
select id, "file_name.png" from prefix_table;
In CI, by using active records, I code that with:
$this->db->select('id, "file_name.png"', FALSE)->from('prefix_table');
but what I got is:
select id, prefix_"file_name.png" from prefix_table;
Is there any way to use the table prefix optional? Or may be, how do I do not use the prefix when selecting using active records?
This is a limitation/bug in CodeIgniter right now -- you won't be able to use a string like that without the prefix butting in. I'd suggest writing the query manually. I've opened an issue on Github for it.
Also, you should use an AS column definition when selecting a string like that, otherwise the string name will also be the column name, and you'll end up with something like:
array(
'id' => 2,
'file_name.png' => 'file_name.png'
)