What is the maximum number of returned expressions allowed in a PostgreSQL SELECT statement?
(Not to be confused with the maximum number of columns in a table.)
I found it programmatically: 1664 (version 13).
The limit is a bit higher that the column limit of 1600. This is the error that I get when crossing the limit:
ERROR: target lists can have at most 1664 entries
The limit is defined in "src/include/access/htup_details.h" (MaxTupleAttributeNumber 1664) next to the column-amount limit (MaxHeapAttributeNumber 1600). The reason for the difference between the two limits is unclear to me.
Related
I am using fuzzystrmatch extension in Postgresql 14.
When I am running below query, it is giving this error message:
ERROR: levenshtein argument exceeds maximum length of 255 characters
SELECT levenshtein('xxxxxxxx', 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY');
Referred this document, https://www.postgresql.org/docs/current/fuzzystrmatch.html
which says, that Both source and target can be any non-null string, with a maximum of 255 characters.
But I have this requirement to support any number of characters for levenshtein. Is there any way, I can update this max length in Postgresql for levenshtein?
I referred few Postgresql and fuzzystrmatch documents which says that we can't have more than 255 characters.
https://www.postgresql.org/docs/current/fuzzystrmatch.html
But I am looking for a way, if this max length can be controlled in Postgresql.
I was doing some tests on Postgres using the tinyint extension when I came across something surprising regarding its range. On typing select -128::tinyint it gave me an ERROR: tinyint out of range message which was not what I was expecting at all.
Assuming negative numbers should be 1 greater (or is it less) than the positive maximum (127 for single byte integers) I thought it was a bug with the extension, however on trying this with non-extended numbers I found exactly the same thing was happening.
select -32768::smallint -> out of range
select -2147483648::integer -> out of range
select -9223372036854775808::bigint -> out of range
Referring to the numeric data type documentation (https://www.postgresql.org/docs/current/datatype-numeric.html)
these numbers should all be possible - all negative numbers one less -32767, -2147483647, -9223372036854775807 work correctly so I am curious as to why this is happening, or does this even happen with other peoples copies.
I tried using both postgresql 10 and postgresql 11 on a ubuntu 16.x desktop.
I think this is because the cast operator :: has a higher precedence that the minus sign.
So -32768::smallint is executed as -1 * 32768::smallint which indeed is invalid.
Using parentheses fixes this: (-32768)::smallint or using the SQL standard cast() operator: cast(-32768 as smallint)
My report processes millions of records. When the number of rows gets too high, I get this error:
The number of rows or columns is too big. Try limiting the number of unique group values.
Details: The number of rows or columns exceeds its limit, 65535.
How can I work around (or increase) this limit?
This error is pretty straightforward. 65535 is 0xFFFF in hexadecimal, so once you hit that limit there's no more vacancies and the hotel is closed. Solutions include:
Reduce the number of rows displayed by using grouping in your crosstab or whatever.
Reduce the amount of incoming data to your report with Record Selection. (Parameters)
Perform the dependent calculations in a custom SQL statement, generated as a temporary table in your report. You can then pass the results into your report as fields, rather than having to print millions of lines.
From every references that I search how to do cumulative sum / running total. they said it's better using windows function, so I did
select grandtotal,sum(grandtotal)over(order by agentname) from call
but I realize that the results are okay as long as the value of each rows are different. Here is the result :
Is There anyway to fix this?
You might want to review the documentation on window specifications (which is here). The default is "range between" which defines the range by the values in the row. You want "rows between":
select grandtotal,
sum(grandtotal) over (order by agentname rows between unbounded preceding and current row)
from call;
Alternatively, you could include an id column in the sort to guarantee uniqueness and not have to deal with the issue of equal key values.
I'm trying to fetch the n-th row of a query result. Further posts suggested the use of OFFSET or LIMIT but those forbid the use of variables (ERROR: argument of OFFSET must not contain variables). Further I read about the usage of cursors but I'm not quite sure how to use them even after reading their PostgreSQL manpage. Any other suggestions or examples for how to use cursors?
My main goal is to calculate the p-quantile of a row and since PostgreSQL doesn't provide this function by default I have to write it on my own.
Cheers
The following returns the 5th row of a result set:
select *
from (
select <column_list>,
row_number() over (order by some_sort_column) as rn
) t
where rn = 5;
You have to include an order by because otherwise the concept of "5th row" doesn't make sense.
You mention "use of variable" so I'm not sure what you are actually trying to achive. But you should be able to supply the value 5 as a variable for this query (or even a sub-select).
You might also want to dig further into windowing functions. Because with that you could e.g. do a sum() over the 3 rows before the current row (or similar constructs) - which could also be useful for you.
if you would like to get 10th record, below query also work fine.
select * from table_name order by sort_column limit 1 offset 9
OFFSET simply skip that many rows before beginning to return rows as mentioned in LIMIT clause.