Haskell SQLite3 query all
Would like to determine the size of a table (length) to avoid a user entering an incremental ID that already exists (Note: left all Haskell books to get my feet wet). Got a table with id, task, date_in, date_out and need to count the number id's. Using this function:
checkUniqueID = do
conn <- open "taglist.db"
len <- query conn "SELECT * FROM task;" (Only xxx) :: IO [id]
let showLength = length $ len
print showLength
close conn
return ()
However: omitting the 'Only' will result in ghci mentioning too few arguments, but I really cannot figure out what to put at xxx. Too bad all Haskell doc is so fragmented, since it is such a cool language.
Thanks guys!
sqlite haskell
asked Nov 22 at 17:50
Madderote
20119
add a comment |
Would like to determine the size of a table (length) to avoid a user entering an incremental ID that already exists (Note: left all Haskell books to get my feet wet). Got a table with id, task, date_in, date_out and need to count the number id's. Using this function:
checkUniqueID = do
conn <- open "taglist.db"
len <- query conn "SELECT * FROM task;" (Only xxx) :: IO [id]
let showLength = length $ len
print showLength
close conn
return ()
However: omitting the 'Only' will result in ghci mentioning too few arguments, but I really cannot figure out what to put at xxx. Too bad all Haskell doc is so fragmented, since it is such a cool language.
Thanks guys!
sqlite haskell
asked Nov 22 at 17:50
Madderote
20119
add a comment |
Would like to determine the size of a table (length) to avoid a user entering an incremental ID that already exists (Note: left all Haskell books to get my feet wet). Got a table with id, task, date_in, date_out and need to count the number id's. Using this function:
checkUniqueID = do
conn <- open "taglist.db"
len <- query conn "SELECT * FROM task;" (Only xxx) :: IO [id]
let showLength = length $ len
print showLength
close conn
return ()
However: omitting the 'Only' will result in ghci mentioning too few arguments, but I really cannot figure out what to put at xxx. Too bad all Haskell doc is so fragmented, since it is such a cool language.
Thanks guys!
sqlite haskell
asked Nov 22 at 17:50
Madderote
20119
Would like to determine the size of a table (length) to avoid a user entering an incremental ID that already exists (Note: left all Haskell books to get my feet wet). Got a table with id, task, date_in, date_out and need to count the number id's. Using this function:
checkUniqueID = do
conn <- open "taglist.db"
len <- query conn "SELECT * FROM task;" (Only xxx) :: IO [id]
let showLength = length $ len
print showLength
close conn
return ()
However: omitting the 'Only' will result in ghci mentioning too few arguments, but I really cannot figure out what to put at xxx. Too bad all Haskell doc is so fragmented, since it is such a cool language.
Thanks guys!
sqlite haskell
sqlite haskell
asked Nov 22 at 17:50
Madderote
20119
asked Nov 22 at 17:50
Madderote
20119
asked Nov 22 at 17:50
Madderote
20119
asked Nov 22 at 17:50
Madderote
20119
asked Nov 22 at 17:50
Madderote
20119
20119
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
I am not terribly familiar with these libraries. I check the docs
of Database.PostgreSQL.Simple
and found out that, if you don't have arguments to your query, you can use query_ and omit the argument tuple. The examples at the very beginning of the docs are quite helpful.
That being said, your approach looks wrong. You are pulling the whole table from the DB only to count the entries. This is a waste: you should instead use something like select count(*) from .. so that you query for the length only.
This might work: (again, I've never used that library)
[Only len] <- query_ conn "select count(*) from task" :: IO [Only Int]
answered Nov 22 at 18:21
chi
72.8k280135
Hi @Chi with a little change it works. Thanks so much to get me on track again. Library is new for me too and on pulling in the entire table like I did, SQLite throws an error anyway. Maybe if others run into this 'problem' and read your reply, here's the modified code that works:conn <- open "taglist.db"n len <- query_ conn "SELECT (id) FROM task" :: IO [Only Int] let showLength = Data.List.length $ len print showLength close conn return ()
– Madderote
Nov 23 at 7:37
@Madderote If you have a completely working code, you can post it answering your own question. StackOverflow's policy encourage self-answers, when they can be useful to others.
– chi
Nov 23 at 12:27
Thanks for the tip. Will do with future issues, which I will encounter for sure ;-)
– Madderote
Nov 23 at 15:06
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
I am not terribly familiar with these libraries. I check the docs
of Database.PostgreSQL.Simple
and found out that, if you don't have arguments to your query, you can use query_ and omit the argument tuple. The examples at the very beginning of the docs are quite helpful.
That being said, your approach looks wrong. You are pulling the whole table from the DB only to count the entries. This is a waste: you should instead use something like select count(*) from .. so that you query for the length only.
This might work: (again, I've never used that library)
[Only len] <- query_ conn "select count(*) from task" :: IO [Only Int]
answered Nov 22 at 18:21
chi
72.8k280135
Hi @Chi with a little change it works. Thanks so much to get me on track again. Library is new for me too and on pulling in the entire table like I did, SQLite throws an error anyway. Maybe if others run into this 'problem' and read your reply, here's the modified code that works:conn <- open "taglist.db"n len <- query_ conn "SELECT (id) FROM task" :: IO [Only Int] let showLength = Data.List.length $ len print showLength close conn return ()
– Madderote
Nov 23 at 7:37
@Madderote If you have a completely working code, you can post it answering your own question. StackOverflow's policy encourage self-answers, when they can be useful to others.
– chi
Nov 23 at 12:27
Thanks for the tip. Will do with future issues, which I will encounter for sure ;-)
– Madderote
Nov 23 at 15:06
add a comment |
I am not terribly familiar with these libraries. I check the docs
of Database.PostgreSQL.Simple
and found out that, if you don't have arguments to your query, you can use query_ and omit the argument tuple. The examples at the very beginning of the docs are quite helpful.
That being said, your approach looks wrong. You are pulling the whole table from the DB only to count the entries. This is a waste: you should instead use something like select count(*) from .. so that you query for the length only.
This might work: (again, I've never used that library)
[Only len] <- query_ conn "select count(*) from task" :: IO [Only Int]
answered Nov 22 at 18:21
chi
72.8k280135
Hi @Chi with a little change it works. Thanks so much to get me on track again. Library is new for me too and on pulling in the entire table like I did, SQLite throws an error anyway. Maybe if others run into this 'problem' and read your reply, here's the modified code that works:conn <- open "taglist.db"n len <- query_ conn "SELECT (id) FROM task" :: IO [Only Int] let showLength = Data.List.length $ len print showLength close conn return ()
– Madderote
Nov 23 at 7:37
@Madderote If you have a completely working code, you can post it answering your own question. StackOverflow's policy encourage self-answers, when they can be useful to others.
– chi
Nov 23 at 12:27
Thanks for the tip. Will do with future issues, which I will encounter for sure ;-)
– Madderote
Nov 23 at 15:06
add a comment |
I am not terribly familiar with these libraries. I check the docs
of Database.PostgreSQL.Simple
and found out that, if you don't have arguments to your query, you can use query_ and omit the argument tuple. The examples at the very beginning of the docs are quite helpful.
That being said, your approach looks wrong. You are pulling the whole table from the DB only to count the entries. This is a waste: you should instead use something like select count(*) from .. so that you query for the length only.
This might work: (again, I've never used that library)
[Only len] <- query_ conn "select count(*) from task" :: IO [Only Int]
answered Nov 22 at 18:21
chi
72.8k280135
I am not terribly familiar with these libraries. I check the docs
of Database.PostgreSQL.Simple
and found out that, if you don't have arguments to your query, you can use query_ and omit the argument tuple. The examples at the very beginning of the docs are quite helpful.
That being said, your approach looks wrong. You are pulling the whole table from the DB only to count the entries. This is a waste: you should instead use something like select count(*) from .. so that you query for the length only.
This might work: (again, I've never used that library)
[Only len] <- query_ conn "select count(*) from task" :: IO [Only Int]
answered Nov 22 at 18:21
chi
72.8k280135
answered Nov 22 at 18:21
chi
72.8k280135
answered Nov 22 at 18:21
chi
72.8k280135
answered Nov 22 at 18:21
chi
72.8k280135
72.8k280135
Hi @Chi with a little change it works. Thanks so much to get me on track again. Library is new for me too and on pulling in the entire table like I did, SQLite throws an error anyway. Maybe if others run into this 'problem' and read your reply, here's the modified code that works:conn <- open "taglist.db"n len <- query_ conn "SELECT (id) FROM task" :: IO [Only Int] let showLength = Data.List.length $ len print showLength close conn return ()
– Madderote
Nov 23 at 7:37
@Madderote If you have a completely working code, you can post it answering your own question. StackOverflow's policy encourage self-answers, when they can be useful to others.
– chi
Nov 23 at 12:27
Thanks for the tip. Will do with future issues, which I will encounter for sure ;-)
– Madderote
Nov 23 at 15:06
add a comment |
Hi @Chi with a little change it works. Thanks so much to get me on track again. Library is new for me too and on pulling in the entire table like I did, SQLite throws an error anyway. Maybe if others run into this 'problem' and read your reply, here's the modified code that works:conn <- open "taglist.db"n len <- query_ conn "SELECT (id) FROM task" :: IO [Only Int] let showLength = Data.List.length $ len print showLength close conn return ()
– Madderote
Nov 23 at 7:37
@Madderote If you have a completely working code, you can post it answering your own question. StackOverflow's policy encourage self-answers, when they can be useful to others.
– chi
Nov 23 at 12:27
Thanks for the tip. Will do with future issues, which I will encounter for sure ;-)
– Madderote
Nov 23 at 15:06
Hi @Chi with a little change it works. Thanks so much to get me on track again. Library is new for me too and on pulling in the entire table like I did, SQLite throws an error anyway. Maybe if others run into this 'problem' and read your reply, here's the modified code that works:
conn <- open "taglist.db"n len <- query_ conn "SELECT (id) FROM task" :: IO [Only Int] let showLength = Data.List.length $ len print showLength close conn return ()– Madderote
Nov 23 at 7:37
Hi @Chi with a little change it works. Thanks so much to get me on track again. Library is new for me too and on pulling in the entire table like I did, SQLite throws an error anyway. Maybe if others run into this 'problem' and read your reply, here's the modified code that works:
conn <- open "taglist.db"n len <- query_ conn "SELECT (id) FROM task" :: IO [Only Int] let showLength = Data.List.length $ len print showLength close conn return ()– Madderote
Nov 23 at 7:37
@Madderote If you have a completely working code, you can post it answering your own question. StackOverflow's policy encourage self-answers, when they can be useful to others.
– chi
Nov 23 at 12:27
@Madderote If you have a completely working code, you can post it answering your own question. StackOverflow's policy encourage self-answers, when they can be useful to others.
– chi
Nov 23 at 12:27
Thanks for the tip. Will do with future issues, which I will encounter for sure ;-)
– Madderote
Nov 23 at 15:06
Thanks for the tip. Will do with future issues, which I will encounter for sure ;-)
– Madderote
Nov 23 at 15:06
add a comment |
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