Loading third-party library mysql failed

[xeweicheng]

luasql = require "luasql.mysql"

--创建环境对象
env = luasql.mysql()

--连接数据库
conn = env:connect("waterlot","root","ctu96jsj","127.0.0.1",3306)

--设置数据库的编码格式
conn:execute"SET NAMES UTF8"

--执行数据库操作
cur = conn:execute("select * from hts_company")

row = cur:fetch({},"a")

--文件对象的创建
file = io.open("hts_company.txt","w+");

while row do
var = string.format("%d %s\n", row.id, row.name)

print(var)

file:write(var)

row = cur:fetch(row,"a")

end

file:close() --关闭文件对象
conn:close() --关闭数据库连接
env:close() --关闭数据库环境

2020-07-14 14:31:02.319 [error] Lua Hook: Failed to load lua script "/var/lib/emqx/scripts/test_mysql.lua" due to error {{lua_error,
{no_module,
<<"luasql.mysql">>,
<<"'./luasql/mysql.lua' './luasql/mysql/init.lua' ">>},
{luerl,
{array,
13,
100,
undefined,
{{{table,
{array,
0,
10,
nil,
10},
{{{{empty,
<<"_G">>,
{tref,
0},
empty,
<<"_VERSION">>,
<<"Lua 5.2">>,
empty},
<<"assert">>,
{function,
#Fun<luerl_lib_basic.0.131962688>},
{empty,
<<"bit32">>,
{tref,
5},
empty},
<<"collectgarbage">>,
{function,
#Fun<luerl_lib_basic.1.131962688>},
{empty,
<<"debug">>

Remark: other self .lua aslo not load by require, sample require("NumConvert")

2020-07-14 14:31:02.316 [error] Lua Hook: Failed to load lua script "/var/lib/emqx/scripts/mcu_api.lua" due to error {{lua_error,
{no_module,
<<"NumConvert">>,
<<"'./NumConvert.lua' './NumConvert/init.lua' ">>},
{luerl,
{array,
13,
100,
undefined,
{{{table,
{array,
0,
10,
nil,
10},