Question

I have the following file “dupeExtracter.rb” to remove duplicate entries from a DB table that is throwing an exception when I run it:

require 'sqlite3'

 db = SQLite3::Database.new('development.sqlite3')
 db.results_as_hash = true;

 #This query will return the lowest id of every entry that occurs more than once in the   DB
 #Entries that occur only once will NOT be in this resultset
 #In other words this query will return the lowest id of every Duplicate in the DB
 #It takes all these entries and populates the duplicates table with them
 rows = db.execute("SELECT L1.* FROM listings L1
 WHERE L1.id = 
 (SELECT MIN(L2.id) FROM Listings L2 WHERE 
 L1.name = L2.name 
 AND L1.telephone = L2.telephone
 AND L1.latitude = L2.latitude
 AND L1.longitude = L2.longitude)
 ") 


rows.each do |row|

   db.execute("DELETE FROM listings L
   WHERE L.id <> row['id']
   AND L.name = row['name']
   AND L.telephone = row['telephone']
   AND L.latitude = row['latitude']
   AND L.longitude = row['longitude']
  ")

 end

This is the exception:

/Users/AM/.rvm/gems/ruby-1.9.2-p290/gems/sqlite3-1.3.5/lib/sqlite3/database.rb:91:in `initialize': near "L": syntax error (SQLite3::SQLException)
from /Users/AM/.rvm/gems/ruby-1.9.2-p290/gems/sqlite3-1.3.5/lib/sqlite3/database.rb:91:in `new'
from /Users/AM/.rvm/gems/ruby-1.9.2-p290/gems/sqlite3-1.3.5/lib/sqlite3/database.rb:91:in `prepare'
from /Users/AM/.rvm/gems/ruby-1.9.2-p290/gems/sqlite3-1.3.5/lib/sqlite3/database.rb:134:in `execute'
from dupeExtracter.rb:22:in `block in <main>'
from dupeExtracter.rb:20:in `each'
from dupeExtracter.rb:20:in `<main>'

Im not sure how to debug it or fix it. Tried a couple of ways but it seems to not work.

Please help

EDIT changed the loop above to this after one of the answers below suggested this. But Im still getting an exception:

rows.each do |row|

db.execute("DELETE FROM listings 
WHERE id <> row['id']
AND name = row['name']
AND telephone = row['telephone']
AND latitude = row['latitude']
AND longitude = row['longitude']
")

Exception:

/Users/AM/.rvm/gems/ruby-1.9.2-p290/gems/sqlite3-1.3.5/lib/sqlite3/database.rb:91:in `initialize': near "['id']": syntax error (SQLite3::SQLException)
from /Users/AM/.rvm/gems/ruby-1.9.2-p290/gems/sqlite3-1.3.5/lib/sqlite3/database.rb:91:in `new'
from /Users/AM/.rvm/gems/ruby-1.9.2-p290/gems/sqlite3-1.3.5/lib/sqlite3/database.rb:91:in `prepare'
from /Users/AM/.rvm/gems/ruby-1.9.2-p290/gems/sqlite3-1.3.5/lib/sqlite3/database.rb:134:in `execute'
from dupeExtracter.rb:22:in `block in <main>'
from dupeExtracter.rb:20:in `each'
from dupeExtracter.rb:20:in `<main>'

Answer 1

Since the exception tells you that there’s an error near the token “L”, and there’s only one instance of this token in your SQL, it appears to me that SQLite does not accept the alias on the DELETE statement. A quick check of the syntax diagram indicates that, indeed, no alias is allowed for DELETE.

But consider doing this in one statement:

DELETE FROM listings WHERE EXISTS
   (SELECT * FROM Listings L2 
       WHERE id      < listings.id
       AND name      = listings.name
       AND telephone = listings.telephone
       AND latitude  = listings.latitude
       AND longitude = listings.longitude)

This will delete every record in listings that has a similar record in the listings table with a lower id (that is, all but the lowest id row for every cohort).