I'm trying to figure out how to involve NEWID() (so I can return the results in a random order) in a CASE statement with in the ORDER BY clause, like so:
ORDER BY CASE WHEN #RankingMethod = 1 THEN intFoo ELSE NEWID() END DESC
Obviously this doesn't work, as it throws "Operand type clash: uniqueidentifier is incompatible with int"
Is there a way to construct this ORDER BY to have it either sort randomly or by a specified column?
You could do
ORDER BY CASE WHEN #RankingMethod = 1 THEN intFoo ELSE -1 END DESC, newid()
If needed, choose another "magic value" instead of -1
Related
What is the argument type for the order by clause in Postgresql?
I came across a very strange behaviour (using Postgresql 9.5). Namely, the query
select * from unnest(array[1,4,3,2]) as x order by 1;
produces 1,2,3,4 as expected. However the query
select * from unnest(array[1,4,3,2]) as x order by 1::int;
produces 1,4,3,2, which seems strange. Similarly, whenever I replace 1::int with whatever function (e.g. greatest(0,1)) or even case operator, the results are unordered (on the contrary to what I would expect).
So which type should an argument of order by have, and how do I get the expected behaviour?
This is expected (and documented) behaviour:
A sort_expression can also be the column label or number of an output column
So the expression:
order by 1
sorts by the first column of the result set (as defined by the SQL standard)
However the expression:
order by 1::int
sorts by the constant value 1, it's essentially the same as:
order by 'foo'
By using a constant value for the order by all rows have the same sort value and thus aren't really sorted.
To sort by an expression, just use that:
order by
case
when some_column = 'foo' then 1
when some_column = 'bar' then 2
else 3
end
The above sorts the result based on the result of the case expression.
Actually I have a function with an integer argument which indicates the column to be used in the order by clause.
In a case when all columns are of the same type, this can work: :
SELECT ....
ORDER BY
CASE function_to_get_a_column_number()
WHEN 1 THEN column1
WHEN 2 THEN column2
.....
WHEN 1235 THEN column1235
END
If columns are of different types, you can try:
SELECT ....
ORDER BY
CASE function_to_get_a_column_number()
WHEN 1 THEN column1::varchar
WHEN 2 THEN column2::varchar
.....
WHEN 1235 THEN column1235::varchar
END
But these "workarounds" are horrible. You need some other approach than the function returning a column number.
Maybe a dynamic SQL ?
I would say that dynamic SQL (thanks #kordirko and the others for the hints) is the best solution to the problem I originally had in mind:
create temp table my_data (
id serial,
val text
);
insert into my_data(id, val)
values (default, 'a'), (default, 'c'), (default, 'd'), (default, 'b');
create function fetch_my_data(col text)
returns setof my_data as
$f$
begin
return query execute $$
select * from my_data
order by $$|| quote_ident(col);
end
$f$ language plpgsql;
select * from fetch_my_data('val'); -- order by val
select * from fetch_my_data('id'); -- order by id
In the beginning I thought this could be achieved using case expression in the argument of the order by clause - the sort_expression. And here comes the tricky part which confused me: when sort_expression is a kind of identifier (name of a column or a number of a column), the corresponding column is used when ordering the results. But when sort_expression is some value, we actually order the results using that value itself (computed for each row). This is #a_horse_with_no_name's answer rephrased.
So when I queried ... order by 1::int, in a way I have assigned value 1 to each row and then tried to sort an array of ones, which clearly is useless.
There are some workarounds without dynamic queries, but they require writing more code and do not seem to have any significant advantages.
I have the following case statement to prepare as a dynamic as shown below:
Example:
I have the case statement:
case cola
when cola between '2001-01-01' and '2001-01-05' then 'G1'
when cola between '2001-01-10' and '2001-01-15' then 'G2'
when cola between '2001-01-20' and '2001-01-25' then 'G3'
when cola between '2001-02-01' and '2001-02-05' then 'G4'
when cola between '2001-02-10' and '2001-02-15' then 'G5'
else ''
end
Note: Now I want to create dynamic case statement because of the values dates and name passing as a parameter and it may change.
Declare
dates varchar = '2001-01-01to2001-01-05,2001-01-10to2001-01-15,
2001-01-20to2001-01-25,2001-02-01to2001-02-05,
2001-02-10to2001-02-15';
names varchar = 'G1,G2,G3,G4,G5';
The values in the variables may change as per the requirements, it will be dynamic. So the case statement should be dynamic without using loop.
You may not need any function for this, just join to a mapping data-set:
with cola_map(low, high, value) as (
values(date '2001-01-01', date '2001-01-05', 'G1'),
('2001-01-10', '2001-01-15', 'G2'),
('2001-01-20', '2001-01-25', 'G3'),
('2001-02-01', '2001-02-05', 'G4'),
('2001-02-10', '2001-02-15', 'G5')
-- you can include as many rows, as you want
)
select table_name.*,
coalesce(cola_map.value, '') -- else branch from case expression
from table_name
left join cola_map on table_name.cola between cola_map.low and cola_map.high
If your date ranges could collide, you can use DISTINCT ON or GROUP BY to avoid row duplication.
Note: you can use a simple sub-select too, I used a CTE, because it's more readable.
Edit: passing these data (as a single parameter) can be achieved by passing a multi-dimensional array (or an array of row-values, but that requires you to have a distinct, predefined composite type).
Passing arrays as parameters can depend on the actual client (& driver) you use, but in general, you can use the array's input representation:
-- sql
with cola_map(low, high, value) as (
select d[1]::date, d[2]::date, d[3]
from unnest(?::text[][]) d
)
select table_name.*,
coalesce(cola_map.value, '') -- else branch from case expression
from table_name
left join cola_map on table_name.cola between cola_map.low and cola_map.high
// client pseudo code
query = db.prepare(sql);
query.bind(1, "{{2001-01-10,2001-01-15,G2},{2001-01-20,2001-01-25,G3}}");
query.execute();
Passing each chunk of data separately is also possible with some clients (or with some abstractions), but this is highly depends on your driver/orm/etc. you use.
I need to further refine my stored proc resultset from this post, I need to filter my resultset to display only records where emailaddr is NULL (meaning display only records that have Invoice_DeliveryType value of 'N' ).
Among numerous queries, I have tried:
select
Invoice_ID, 'Unknown' as Invoice_Status,
case when Invoice_Printed is null then '' else 'Y' end as Invoice_Printed,
case when Invoice_DeliveryDate is null then '' else 'Y' end as Invoice_Delivered,
(case when Invoice_DeliveryType <> 'USPS' then ''
when exists (Select 1
from dbo.Client c
Where c.Client_ID = SUBSTRING(i.Invoice_ID, 1, 6) and
c.emailaddr is not null
)
then 'Y'
else 'N'
end)
Invoice_ContactLName + ', ' + Invoice_ContactFName as ContactName,
from
dbo.Invoice
left outer join
dbo.fnInvoiceCurrentStatus() on Invoice_ID = CUST_InvoiceID
where
CUST_StatusID = 7
AND Invoice_ID = dbo.Client.Client_ID
AND dbo.client.emailaddr is NULL
order by
Inv_Created
but I get an error
The conversion of the nvarchar value '20111028995999' overflowed an int column
How can I get the stored procedure to only return records with DeliveryType = 'N' ?
Trying selecting the stored proc results into a temp table, then select
* from #TempTable
We could really do with a schema definition to get this problem resolved.
It appears that there is an implicit conversion occurring within one of your case statements, but without the schema def's it's difficult to track down which one.
You can't safely mix datatypes in CASE expressions, unless you are absolutely sure that any implicit conversions will work out OK you should make the conversions explicit.
Judging by the error message seeming to include something that could be a date represented as a string(20111028) plus some kind of other data ?time?(995999) it may be something to do with Invoice_DeliveryDate, but this is a shot in the dark without more details.
I have a table with a varchar column, and I want to find values that match a certain number. So lets say that column contains the following entries (except with millions of rows in real life):
123456789012
2345678
3456
23 45
713?2
00123456789012
So I decide I want all the rows which are numerically 123456789012 write a statement that looks something like this:
SELECT * FROM MyTable WHERE CAST(MyColumn as bigint) = 123456789012
It should return the first and last row, but instead the whole query blows up because it can't convert the "23 45" and "713?2" to bigint.
Is there another way to do the conversion that will return NULL for values that can't convert?
SQL Server does NOT guarantee boolean operator short-circuit, see On SQL Server boolean operator short-circuit. So all solution using ISNUMERIC(...) AND CAST(...) are fundamentally flawed (they may work, but hey can arbitrarily fail later dependiong on the generated plan). A better solution is using CASE, as Thomas suggests: CASE ISNUMERIC(...) WHEN 1 THEN CAST(...) ELSE NULL END. But, as gbn pointed out, ISNUMERIC is notoriously finicky in identifying what 'numeric' means and many cases where one would expect it to return 0 it returns 1. So mixing the CASE with the LIKE:
CASE WHEN MyRow NOT LIKE '%[^0-9]%' THEN CAST(MyRow as bigint) ELSE NULL END
But the real problem is that if you have millions of rows and you have to search them like this, you'll always end up scanning end-to-end since the expression is not SARG-able (no matter how we rewrite it). The real issue here is data purity, and should be addressed at the appropriate level, where the data is populated. Another thing to consider is if is possible to create a persisted computed column with this expression and create a filtered index on it which eliminates NULL (ie. non-numeric). That would speed up things a little.
If you are using SQL Server 2012 you can use the 2 new methods:
TRY_CAST()
TRY_CONVERT()
Both methods are equivalent. They return a value cast to the specified data type if the cast succeeds; otherwise, returns null. The only difference is that CONVERT is SQL Server specific, CAST is ANSI. using CAST will make your code more portable (although not sure if any other database provider implements TRY_CAST)
ISNUMERIC will accept empty string and values like 1.23 or 5E-04 so could be unreliable.
And you don't know what order things will be evaluated in so it could still fail (SQL is declarative, not procedural, so the WHERE clause probably won't be evaluated left to right)
So:
you want to accept value that consist only of the characters 0-9
you need to materialise the "number" filter so it's applied before CAST
Something like:
SELECT
*
FROM
(
SELECT TOP 2000000000 *
FROM MyTable
WHERE MyColumn NOT LIKE '%[^0-9]%' --double negative rejects anything except 0-9
ORDER BY MyColumn
) foo
WHERE
CAST(MyColumn as bigint) = 123456789012 --applied after number check
Edit: quick example that fails.
CREATE TABLE #foo (bigintstring varchar(100))
INSERT #foo (bigintstring )VALUES ('1.23')
INSERT #foo (bigintstring )VALUES ('1 23')
INSERT #foo (bigintstring )VALUES ('123')
SELECT * FROM #foo
WHERE
ISNUMERIC(bigintstring) = 1
AND
CAST(bigintstring AS bigint) = 123
SELECT *
FROM MyTable
WHERE ISNUMERIC(MyRow) = 1
AND CAST(MyRow as float) = 123456789012
The ISNUMERIC() function should give you what you need.
SELECT * FROM MyTable
WHERE ISNUMERIC(MyRow) = 1
AND CAST(MyRow as bigint) = 123456789012
And to add a case statement like Thomas suggested:
SELECT * FROM MyTable
WHERE CASE(ISNUMERIC(MyRow)
WHEN 1 THEN CAST(MyRow as bigint)
ELSE NULL
END = 123456789012
http://msdn.microsoft.com/en-us/library/ms186272.aspx
SELECT *
FROM MyTable
WHERE (ISNUMERIC(MyColumn) = 1) AND (CAST(MyColumn as bigint) = 123456789012)
Additionally you can use a CASE statement in order to get null values.
SELECT
CASE
WHEN (ISNUMERIC(MyColumn) = 1) THEN CAST(MyColumn as bigint)
ELSE NULL
END AS 'MyColumnAsBigInt'
FROM tableName
If you require additional filtering, for numerics which are not valid to be cast to bigint, you can use the following instead of ISNUMERIC:
PATINDEX('%[^0-9]%',MyColumn)) = 0
If you need decimal values instead of integers, cast to float instead and change the regex to '%[^0-9.]%'
I have written a recursive function and depending on the output I need to select different fields. My question is now, how can I do this multiple times without having to call the function more then once? What I'm doing right now is just using the CASE WHEN... condition and checking every time what the functions return. (This is only a pseudo code and doesn't do anything real, it's just for understanding)
SELECT
id,
(CASE WHEN (function(id) > 0)
THEN field1
ELSE field2
END) as value1,
(CASE WHEN (function(id) > 0)
THEN field3
ELSE field4
END) as value2,
(CASE WHEN (function(id) > 0)
THEN field5
ELSE field6
END) as value3
FROM table1
...
How can I optimize this query and call the function only once?
Thanks in advance!
If the function is declared IMMUTABLE, it is safe to call it many times, as it will not be reevaluated.
From the docs:
IMMUTABLE indicates that the function cannot modify the database and always returns the same result when given the same argument values; that is, it does not do database lookups or otherwise use information not directly present in its argument list. If this option is given, any call of the function with all-constant arguments can be immediately replaced with the function value.
use a subquery :
SELECT foo, bar, result
FROM (
SELECT ..., function(id) AS result
....
) as tmp
You may be able to use some funky tuple thing like:
SELECT id,
CASE WHEN function(id) > 0
THEN (field1, field3, field5)
ELSE (field2, field4, field6)
END as (value1, value2, value3)
but I have no experience with this syntax