sql: refine description for `EXPLAIN` (#1324)
sql: refine description for `EXPLAIN` (#1324)

* sql: fix description for `EXPLAIN`

* Update sql/util.md

Co-Authored-By: Lilian Lee <c684465c17314189c18707959627e2ec4fdec2d0@pingcap.com>

* Update sql/util.md

Co-Authored-By: Lilian Lee <c684465c17314189c18707959627e2ec4fdec2d0@pingcap.com>

pingcap/docs-cn,pingcap/docs-cn