How to check duplicate item in column in sqlite phonegap

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SQL

PhoneGap

need to check duplicate item in my table before insert date .But i am getting error while checking.Here is my code.I need to check whether the element already exist then return false If not then return true.And create a new entry

function validationField() {
     db.transaction(getallTableCntend, errorCB);
   }

   function getallTableCntend(tx) {
       tx.executeSql('SELECT * FROM CaseTable', [], queryexcecute, errorCB);
   }
   function queryexcecute(tx, result) {
       var len = result.rows.length;

       for (var i = 0; i < len; i++) {
         if(result.rows.item(i).CaseName ==$('.caseName_h').val()){
           alert("Folder is already Exit.");
           isvalid=false;
           Break;
           return;;
         }
       }
      }

I am calling this like this.

$(document).on('click', '#AddButton', function() {
     isvalid = validationField();
    if (isvalid) {
            insertData();
            window.requestFileSystem(LocalFileSystem.PERSISTENT, 0, onFileSystemSuccess, onFileSystemFail);
    }
});