code: func (kv *KeyValue) sql(sqlStmt string) string {
  	// string manipulation is done only once
  	kv.queriesInitOnce.Do(func() {
  		kv.queries = make(map[string]string, 8) // we have 8 queries in this file
  		kv.replacer = strings.NewReplacer("/*TPRE*/", kv.TablePrefix)
  	})
  	kv.queriesMu.RLock()
  	sqlQuery, ok := kv.queries[sqlStmt]
  	kv.queriesMu.RUnlock()
  	if ok {
  		return sqlQuery
  	}
  	kv.queriesMu.Lock()
  	// check again, now holding the lock
  	if sqlQuery, ok = kv.queries[sqlStmt]; ok {
  		kv.queriesMu.Unlock()
  		return sqlQuery
  	}
  	sqlQuery = sqlStmt
  	if f := kv.PlaceHolderFunc; f != nil {
  		sqlQuery = f(sqlQuery)
  	}
  	sqlQuery = kv.replacer.Replace(sqlQuery)
  	kv.queries[sqlStmt] = sqlQuery
  	kv.queriesMu.Unlock()
  	return sqlQuery
  }
docs: // sql returns the query, replacing placeholders using PlaceHolderFunc,
  // and /*TPRE*/ with TablePrefix.