String attributes can store arbitrary strings attached to every document. There's a fixed size limit of 4 MB per value. Also, searchd will currently cache all the values in RAM, which is an additional implicit limit.

As of 1.10-beta, strings can only be used for storage and retrieval. They can not participate in expressions, be used for filtering, sorting, or grouping (ie. in WHERE, ORDER or GROUP clauses). Note that attributes declared using sql_attr_string will not be full-text indexed; you can use sql_field_string directive for that.

出现结果为0，可以先用shell 调试下即bin/search 看看返回的结果是不是0。如果正确，则看下你用sphinxapi.php这个是不是旧的，也应该更新为新的。