Avoid duplicate rows in phonegap database - sql

Question

I have a database with a single column and create it like this
function populateDB(tx){
tx.executeSql('CREATE TABLE IF NOT EXISTS RESULT(result, UNIQUE(result))');
}
however, when I want to write objects into the table, I get the error:
could not execute statement (19 constraint failed)
The error only appears when I add the NOT NULL and PRIMARY KEY to the set-Up. Without it, it keeps writing duplicates in my database (I fill the database with data from a webservice on startup of a phonegap iOS application, so I want to catch duplicate rows on database level)
At first I had only "PRIMARY KEY" in it, and because the error says something about constraints, I was assuming the primary key has to be "NOT NULL", adding it to the code, I still got the same error.
how can I solve this. thanks in advance
edit: Maybe it´s important for you to know that I write stringyfied JSON Objects into the results column.
edit: I insert the object in this function. Basically I do it one by one:
this.save = function(){
db.transaction (function(transaction){
object = $.toJSON(self);
object = encodeURI(object);
transaction.executeSql('INSERT INTO RESULT (result) VALUES ("'+object+'")');
},
errorCB,
successCB
);
}
edit: I updated my set up table code. The error doesnt occur on every row, but the objects are actually unique.

Answer 1

"IF NOT EXISTS" is the catch here. You get constraint failed when you use conditions like "IF NOT EXISTS" or "REPLACE", "IGNORE" etc in SQLite queries.
Suppose, you're trying to create a table that already exists, then the constraint (here not creating the table again if it already exist) fails and hence the query fails (which you actually want - you dont want to duplicate the tables right?) and gives you the error constraint failed.
You may get a similar error on INSERT or REPLACE, INSERT or IGNORE, etc...