code: func (b *PlanBuilder) GetDBTableInfo() []stmtctx.TableEntry {
  	var tables []stmtctx.TableEntry
  	existsFunc := func(tbls []stmtctx.TableEntry, tbl *stmtctx.TableEntry) bool {
  		for _, t := range tbls {
  			if t == *tbl {
  				return true
  			}
  		}
  		return false
  	}
  	for _, v := range b.visitInfo {
  		tbl := &stmtctx.TableEntry{DB: v.db, Table: v.table}
  		if !existsFunc(tables, tbl) {
  			tables = append(tables, *tbl)
  		}
  	}
  	return tables
  }
docs: // GetDBTableInfo gets the accessed dbs and tables info.