I have the following WHERE clause on a table x with column 1 as integer.
The SELECT is called in a function with parameters (a integer, b integer)
Call the function:
SELECT * FROM function(0, 10)
Script in funcion:
SELECT * FROM tablex x WHERE x.column1 between a and b
Now i miss the results where column1 is null, but in this case it is important to get these. Depends who calls the function. What should be parameter "a" to also get the null values. Or is there a way to disable the where clause depending on the paramter which are coming?
I found a nice solution for this:
SELECT * FROM tablex x WHERE coalesce(x.column1, 0) between a and b
Add logic to admit null column1 values:
SELECT *
FROM tablex x
WHERE x.column1 BETWEEN a AND b OR x.column1 IS NULL;
To make the NULLs behave as actual values, invert the logic.
[and add a comment to the code, because the negation might confuse future readers/maintainers]:
SELECT * FROM tablex x WHERE NOT x.column1 < a and NOT x.column1 >= b;
Note the above assumes you want NULLs in both a and b to be treated as -inf and +inf , respectively.
Related
I want to update multiple columns in table which are conditionally dependent on each other.
create table justtable(a numeric, b numeric, c numeric,d numeric,e numeric)
insert into justtable values(1,10,10,10,10)
select * from justtable
returns - 1;10;10;10;10
update justtable set b=10, c=b*2, d=c*2, e=d*2 where a=1;
select * from justtable
returns - 1;10;20;20;20
I want it to return 1;10;20;40;80.
Is it possible to do this is single query else will have to write multiple updates in sequence. Please suggest.
In your case, I would use some arithmetic to rewrite the query, the b column is the minimum base for arithmetic, so we might get formulas like below.
c = 2 * b
d = 4 * b
e = 8 * b
you can try to use this
update justtable
set b=10, c=b*2, d=b*4, e=b*8
where a=1;
sqlfiddle
Here's a short code sample that behaves unexpectedly for me in PostgreSQL v9.5:
create table test (a boolean, b boolean);
insert into test (a) values ('true'),('true'),('true'),('true'),('true');
update test set b = rand.val from (select random() > 0.5 as val from test) as rand;
I expect column b to take on random true/false values, but for some reason it's always false. If I run the subselect of:
select random() > 0.5 as val from test;
It returns random true/false combinations as I want. But for some reason once I try to update the actual table it fails. I've tried several casting combinations but it doesn't seem to help.
What am I missing here?
How about:
update test set b = (random() > 0.5);
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.
If I have a table MyTable with columns a,b and c, which are ints. Given that I want to update all 'a's based on the values of b and c.
Update MyTable set a = 2 where b = 1 and c = 1
It's far too late, and I cannot for the life of me see why this statement doesn't work, am I missing something silly?
Edit, woops, forgot the error.
"Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression."
Edit2: That was the exact query I was using (different column names). Turns out there was a trigger on the table which was broken. I feel a little silly now, but thanks for the help anyway :)
There's nothing wrong with the statement you posted. The error is elsewhere.
Could you have posted the wrong query? Or perhaps you over-simplified it? A subquery looks something like this:
UPDATE MyTable
SET a = 2
WHERE b = 1 AND c = (SELECT c FROM MyTable2 WHERE id = 5)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ <--- subquery
An invalid query that could give the error message you get could look like this:
UPDATE MyTable
SET a = 2
WHERE b = 1 AND c = (SELECT c, d FROM MyTable2 WHERE id = 5)
The second query is invalid because it returns two values but the = operator only allows comparison to a single value.
The solution is to ensure that all subqueries used in equality comparisons only return a single row consisting of a single column.
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.]%'