Vue中使用vxe-table组件分页查询，多页选择数据回显，分页记录保存选中的数据

官方示例：vxe-table v3https://vxetable.cn/v3/#/table/advanced/page

 当表格中需要渲染的数据量比较大，有几万几十万条数据时，在前端分页将会非常慢，建议将当前页码和每页数量传递个后端，后端分好后给前端渲染。

后端查询SQL时，通过limit 和offset 查询分页：

sql += ` limit ${pageSize} offset ${pageSize * (currentPage - 1)} `

后端除了返回要显示的页数据外，通常还要传递总数量total：

router.get('/', async (ctx, next) => {
  let { task_info, state, currentPage, pageSize, check_host_name_alias, need_update_tile, priority, check_progress, download_progress, downloadfialdcount, check_faild_count } = ctx.request.query
  let sql = `select * from (
SELECT
   SUBSTRING (task_info, 1, 11) as task_info_substring,
	( SELECT NAME FROM downloaduser WHERE machine_code = T.check_host_name ) AS "check_host_name_alias",
	( SELECT NAME FROM downloaduser WHERE machine_code = T.download_host_name ) AS "download_host_name_alias",
	( CASE T.STATE WHEN 1 THEN now( ) - T.check_start_time ELSE T.check_end_time - T.check_start_time END ) AS "check_use_time",
	( CASE T.STATE WHEN 4 THEN now( ) - T.download_start_time ELSE T.download_end_time - T.check_start_time END ) AS "download_use_time",
	* 
FROM
	task T ) t2 where 1=1`
  if (task_info) {
    // console.log("task_info:", task_info)
    let task_info_arr = task_info.split("\n")


    sql += ` and t2.task_info_substring in (${format_arr_to_str(task_info_arr)})`
  }
  if (state) {
    sql += ` and state = ${state}`
  }
  if (need_update_tile) {
    sql += ` and need_update_tile  like '%${need_update_tile}%'`
  }

  // sql += ' order by task_info asc'
  // 多字段排序
  // if (priority) {
  //   sql += ` ,priority ${priority}`
  // }

  if (priority) {
    sql += ` order by priority ${priority}`
  }
  let data_count = await db.query(`select count(*) from (${sql}) t_temp`);//满足条件的记录总数
  let total = parseInt(data_count.rows[0].count)

  sql += ` limit ${pageSize} offset ${pageSize * (currentPage - 1)} `
  // console.log("sql:", sql)
  let data = await db.query(sql);
  ctx.body = {
    code: 0,
    message: "success",
    data: { ...data, total }
  }
})

注意：这里查询总数量时，是用的`select count(*) from (${sql}) t_temp` ，这样查询速度比较快。如果全表查询，再返回查出的rows.length，这样速度会很慢 

对于多页选择，需要指定row-id=“主键字段”和:checkbox-config="{ reserve: true }"

获取当前页选中的行数据：调用 this.$refs.ref_table_task.getCheckboxRecords()

获取当前页以外选中的行数据：调用 this.$refs.ref_table_task.getCheckboxReserveRecords()

注意：经测试，每页最多选中500行左右，否则在切换回选中的页时会非常卡