unique_field_value Yes Returns FALSE if the value is already used in the target table.

• Target table name can be a literal value 'tbl_target_table' or the name of a constant 'TABLE_TARGET_TABLE'
• Target column is the name of the column that the data is destined for
• UID_col_name is the name of the primary key, usually "id"
• UID input name should be an input name available in either _GET or _POST.

If the value UID input has a value the row with the UID value for the UID_col_name will be ignored in the search. unique_field_value
  [target_table,
   target_column,
   UID_col_name,
   Input name for the UID
  ]