我如何告诉PATCH方法我要更新哪个字段

I'm working on a simple REST API and I'm having troubles with the PATCH method. I don't know how can i tell the method and the query which fields i want to update(for example which fields are passed as JSON) in the database. Here is what i have so far.

func PatchServer(c echo.Context) error {
    patchedServer := new(structs.Server)
    requestID := c.Param("id")
    if err := c.Bind(patchedServer); err != nil {
        return err
    }
        sql := "UPDATE servers SET server_name = CASE WHEN ? IS NOT NULL THEN ? END WHERE id = ?"
        stmt, err := db.Get().Prepare(sql)
    if err != nil {
        panic(err)
    }
    _, err2 := stmt.Exec(patchedServer.Name, patchedServer.Name, requestID)
    if err2 != nil {
        panic(err2)
    }
    fmt.Println(patchedServer.ID, patchedServer.Name, patchedServer.Components)
    fmt.Println("Requested id: ", requestID)
    return c.JSON(http.StatusOK, "Patched!")
    }