diff --git a/spec/query_generator_spec.rb b/spec/query_generator_spec.rb
index 4226f20..af5338c 100644
--- a/spec/query_generator_spec.rb
+++ b/spec/query_generator_spec.rb
@@ -5,91 +5,128 @@ class SqlGeneratorTester
     it 'tests simple search term without column name and without quotes' do
       @query = TextToSqlQuery.new('-123', [:'players.title', :'players.tag', :'players.device_id'], :'players.device_id')
 
-      expect(@query.where_clause).to eq ['players.device_id LIKE ?', '%-123%']
+      expect(@query.where_clause).to eq ['players.device_id ILIKE ?', '%-123%']
     end
 
     it 'tests simple search term with column name and without quotes' do
       @query = TextToSqlQuery.new('title:ab', [:'players.title', :'players.tag', :'players.device_id'], :'players.device_id')
 
-      expect(@query.where_clause).to eq ['players.title LIKE ?', '%ab%']
+      expect(@query.where_clause).to eq ['players.title ILIKE ?', '%ab%']
     end
 
     it 'tests simple search term with unknown column name and without quotes' do
       @query = TextToSqlQuery.new('unknown:ab', [:'players.title', :'players.tag', :'players.device_id'], :'players.device_id')
 
-      expect(@query.where_clause).to eq ['players.device_id LIKE ?', '%ab%']
+      expect { @query.where_clause }.to raise_error(RuntimeError, "Unknown field 'unknown'")
     end
 
     it 'tests simple search term without column name and with quotes' do
-      @query = TextToSqlQuery.new('"ab"', [:'players.title', :'players.tag', :'players.device_id'], :'players.device_id')
+      @query = TextToSqlQuery.new('ab', [:'players.title', :'players.tag', :'players.device_id'], :'players.device_id')
 
-      expect(@query.where_clause).to eq ['players.device_id LIKE ?', '%"ab"%']
+      expect(@query.where_clause).to eq ['players.device_id ILIKE ?', '%ab%']
     end
 
     it 'tests simple search term with column name and with quotes' do
       @query = TextToSqlQuery.new('tag:"ab"', [:'players.title', :'players.tag', :'players.device_id'], :'players.device_id')
 
-      expect(@query.where_clause).to eq ['players.tag LIKE ?', '%"ab"%']
+      expect(@query.where_clause).to eq ['players.tag ILIKE ?', '%ab%']
     end
 
     it 'tests search without operators' do
       @query = TextToSqlQuery.new('123 456', [:'players.title', :'players.tag', :'players.device_id'], :'players.device_id')
 
-      expect(@query.where_clause).to eq ['(players.device_id LIKE ? OR players.device_id LIKE ?)', '%123%', '%456%']
+      expect(@query.where_clause).to eq ['(players.device_id ILIKE ? OR players.device_id ILIKE ?)', '%123%', '%456%']
     end
 
     it 'tests search with OR operator' do
       @query = TextToSqlQuery.new('123 or 456', [:'players.title', :'players.tag', :'players.device_id'], :'players.device_id')
 
-      expect(@query.where_clause).to eq ['(players.device_id LIKE ? OR players.device_id LIKE ?)', '%123%', '%456%']
+      expect(@query.where_clause).to eq ['(players.device_id ILIKE ? OR players.device_id ILIKE ?)', '%123%', '%456%']
     end
 
     it 'tests search with AND operator' do
       @query = TextToSqlQuery.new('123 and 456', [:'players.title', :'players.tag', :'players.device_id'], :'players.device_id')
 
-      expect(@query.where_clause).to eq ['(players.device_id LIKE ? AND players.device_id LIKE ?)', '%123%', '%456%']
+      expect(@query.where_clause).to eq ['(players.device_id ILIKE ? AND players.device_id ILIKE ?)', '%123%', '%456%']
     end
 
     it 'tests search with NOT operator on default column' do
       @query = TextToSqlQuery.new('not 23', [:'players.title', :'players.tag', :'players.device_id'], :'players.device_id')
 
-      expect(@query.where_clause).to eq ['NOT players.device_id LIKE ?', '%23%']
+      expect(@query.where_clause).to eq ['NOT players.device_id ILIKE ?', '%23%']
     end
 
     it 'tests search with NOT operator on non-default column' do
       @query = TextToSqlQuery.new('not tag:23', [:'players.title', :'players.tag', :'players.device_id'], :'players.device_id')
 
-      expect(@query.where_clause).to eq ['NOT players.tag LIKE ?', '%23%']
+      expect(@query.where_clause).to eq ['NOT players.tag ILIKE ?', '%23%']
     end
 
     it 'tests search with mixed logical operators' do
       @query = TextToSqlQuery.new('title:ab and not tag:hf-1', [:'players.title', :'players.tag', :'players.device_id'], :'players.device_id')
 
-      expect(@query.where_clause).to eq ['(players.title LIKE ? AND NOT players.tag LIKE ?)', '%ab%', '%hf-1%']
+      expect(@query.where_clause).to eq ['(players.title ILIKE ? AND NOT players.tag ILIKE ?)', '%ab%', '%hf-1%']
     end
 
     it 'tests search with mixed logical operators without NOT' do
       @query = TextToSqlQuery.new('title:a and title:b or title:c', [:'players.title', :'players.tag', :'players.device_id'], :'players.device_id')
 
-      expect(@query.where_clause).to eq ['((players.title LIKE ? AND players.title LIKE ?) OR players.title LIKE ?)', '%a%', '%b%', '%c%']
+      expect(@query.where_clause).to eq ['((players.title ILIKE ? AND players.title ILIKE ?) OR players.title ILIKE ?)', '%a%', '%b%', '%c%']
     end
 
     it 'tests search with brackets in expression' do
       @query = TextToSqlQuery.new('title:a and (title:b or title:c)', [:'players.title', :'players.tag', :'players.device_id'], :'players.device_id')
 
-      expect(@query.where_clause).to eq ['(players.title LIKE ? AND (players.title LIKE ? OR players.title LIKE ?))', '%a%', '%b%', '%c%']
+      expect(@query.where_clause).to eq ['(players.title ILIKE ? AND (players.title ILIKE ? OR players.title ILIKE ?))', '%a%', '%b%', '%c%']
     end
 
     it 'tests search with brackets in expression and with NOT operator' do
       @query = TextToSqlQuery.new('title:a and not (title:b or title:c)', [:'players.title', :'players.tag', :'players.device_id'], :'players.device_id')
 
-      expect(@query.where_clause).to eq ['(players.title LIKE ? AND NOT (players.title LIKE ? OR players.title LIKE ?))', '%a%', '%b%', '%c%']
+      expect(@query.where_clause).to eq ['(players.title ILIKE ? AND NOT (players.title ILIKE ? OR players.title ILIKE ?))', '%a%', '%b%', '%c%']
     end
 
     it 'tests search with special characters in search term' do
       @query = TextToSqlQuery.new('title:"%a_\"', [:'players.title', :'players.tag', :'players.device_id'], :'players.device_id')
 
-      expect(@query.where_clause).to eq ['players.title LIKE ?', '%"\%a\_\\"%']
+      expect(@query.where_clause).to eq ['players.title ILIKE ?', '%\%a\_\\%']
+    end
+
+    it 'tests search with field mappings' do
+      @query = TextToSqlQuery.new('tags:h1-r', [:'players.title', :'players.name', :'players.device_id'], :'players.device_id', { tags: "tags.name" })
+
+      expect(@query.where_clause).to eq ['tags.name ILIKE ?', '%h1-r%']
+    end
+
+    it 'tests search with field mappings when fields array has same mapping' do
+      @query = TextToSqlQuery.new('tags:hs1-r', [:'players.title', :'players.tags', :'players.device_id'], :'players.device_id', { tags: "tags.name" })
+
+      expect(@query.where_clause).to eq ['tags.name ILIKE ?', '%hs1-r%']
+    end
+
+    it 'tests complex query' do
+      text = '(device_id:"with space" tags:mta no-quotes-id-123)'\
+      'or "id with quotes-5"  and   ( ("id with q 10" or "id with q 20")'\
+      'and ("id with Q 30" "id with Q 40") and not id-without-Q-50)'
+
+      fields = [:'players.title', :'players.name', :'players.device_id']
+      default_field = :'players.device_id'
+      fields_mappings = { tags: 'tags.name' }
+
+      @query = TextToSqlQuery.new(text, fields, default_field, fields_mappings)
+
+      result_expression = '((players.device_id ILIKE ? OR (tags.name ILIKE ? OR players.device_id ILIKE ?)) OR (players.device_id ILIKE ? AND (((players.device_id ILIKE ? OR players.device_id ILIKE ?) AND (players.device_id ILIKE ? OR players.device_id ILIKE ?)) AND NOT players.device_id ILIKE ?)))'
+      result_params = ['%with space%',
+                       '%mta%',
+                       '%no-quotes-id-123%',
+                       '%id with quotes-5%',
+                       '%id with q 10%',
+                       '%id with q 20%',
+                       '%id with Q 30%',
+                       '%id with Q 40%',
+                       '%id-without-Q-50%']
+
+      expect(@query.where_clause).to eq [result_expression, result_params].flatten
     end
   end
 end
\ No newline at end of file
diff --git a/text_to_sql_query.rb b/text_to_sql_query.rb
index 241149a..f0bbce2 100644
--- a/text_to_sql_query.rb
+++ b/text_to_sql_query.rb
@@ -10,6 +10,9 @@ class TextToSqlQuery
       mappings[field_name.to_sym] = field
       mappings
     end)
+    fields_mappings.each do |field, value|
+      @fields_mappings[field] = value if @fields_mappings[field]
+    end
   end
 
   def where_clause
@@ -25,8 +28,8 @@ class TextToSqlQuery
     node_value = tree[first_key]
     case first_key
     when :DEFAULT_COLUMN
-      escaped_node_value = escape_special_chars node_value
-      ["#{@default_field.to_s} LIKE ?", "%#{escaped_node_value}%"]
+      escaped_node_value = handle_special_chars node_value
+      ["#{@default_field.to_s} ILIKE ?", "%#{escaped_node_value}%"]
     when :OPERATOR_OR
       generate_expression_for_logical_operator(:OR, node_value)
     when :OPERATOR_AND
@@ -45,12 +48,12 @@ class TextToSqlQuery
 
     else
       # key is column name
-      escaped_node_value = escape_special_chars node_value
+      escaped_node_value = handle_special_chars node_value
       mapping = @fields_mappings[first_key.to_sym]
       if mapping.nil?
-        ["#{@default_field.to_s} LIKE ?", "%#{escaped_node_value}%"]
+        raise "Unknown field '#{first_key.to_s}'"
       else
-        ["#{mapping.to_s} LIKE ?", "%#{escaped_node_value}%"]
+        ["#{mapping.to_s} ILIKE ?", "%#{escaped_node_value}%"]
       end
     end
   end
@@ -80,8 +83,8 @@ class TextToSqlQuery
     ["(#{first_operand_expression} #{operator.to_s} #{second_operand_expression})"] + first_operand_params + second_operand_params
   end
 
-  def escape_special_chars(text)
-    result = text
+  def handle_special_chars(text)
+    result = text.gsub(/\"/, '')
     result.gsub!(/\_/, '\_')
     result.tr!('\\', '\\')
     result.gsub!(/%/, '\%')