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MySQL client protocol in Lua

local mysql = require'mysql_client'

MySQL client protocol in Lua. Stolen from OpenResty, modified to work with sock and added prepared statements.


local mysql = require'mysql_client'

   host = '',
   port = 3306,
   user = 'bar',
   password = 'baz',
   schema = 'foo',
   charset = 'utf8mb4',
   max_packet_size = 1024 * 1024,

assert(cn:query('drop table if exists cats'))

local res = assert(cn:query('create table cats '
           .. '(id serial primary key, '
           .. 'name varchar(5))'))

local res = assert(cn:query('insert into cats (name) '
   .. "values ('Bob'),(''),(null)"))

print(res.affected_rows, ' rows inserted into table cats ',
      '(last insert id: ', res.insert_id, ')')

require'pp'(assert(cn:query('select * from cats order by id asc', 10)))



mysql.connect(options) -> ok | nil,err,errcode,sqlstate

Connect to a MySQL server.

The options argument is a Lua table holding the following keys:

  • host: server’s IP address (required).
  • port: server’s port (optional, defaults to 3306).
  • user: user name.
  • password: password (optional).
  • schema: the schema to set as current schema (optional).
  • collation: the collation used for the connection (charset is implied by this). * use 'server' to get the server’s collation and charset for the connection.
  • charset: the character set used for the connection. * if collation not set, the default collation for the charset is selected.
  • max_packet_size: the upper limit for the reply packets sent from the server (defaults to 16 MB).
  • ssl: if true, then uses SSL to connect to MySQL (defaults to false). If the server does not have SSL support (or just disabled), the error string “ssl disabled on server” is returned.
  • ssl_verify: if true, then verifies the validity of the server SSL certificate (default is false).
  • to_lua = f(v, col) -> v – custom value converter (defaults to mysql.to_lua).

cn:close() -> 1 | nil,err

Closes the current mysql connection and returns the status.

cn:send_query(query) -> bytes | nil,err

Sends the query to the remote MySQL server without waiting for its replies.

Returns the bytes successfully sent out. Use read_result() to read the replies.

cn:read_result([options]) -> res,nil|'again',cols | nil,err,errcode,sqlstate

Reads in the next result set returned from the server.

The options arg can contain:

  • compact = true – return an array of arrays instead of an array of {column->value} maps.
  • to_array = true – return an array of values for single-column results.
  • null_value = val – value to use for null (defaults to nil).
  • to_lua = f(v, col) -> v – custom value converter.

For queries that return a result set, it returns an array of rows. For other queries it returns a Lua table with information such as the autoincrement value if any and the affected rows.

If more results are following the current result, a second return value 'again' is returned. One should always check this value and call this method again to retrieve more results. This usually happens when the original query contains multiple statements (separated by semicolon in the same query string) or calling a stored procedure.

In case of errors, this method returns at most 4 values: nil, err, errcode, and sqlstate. The err return value contains a string describing the error, the errcode return value holds the MySQL error code (a numerical value), and finally, the sqlstate return value contains the standard SQL error code that consists of 5 characters. Note that, the errcode and sqlstate might be nil if MySQL does not return them.

NOTE: 64 bit integers and decimals are converted to Lua numbers by default. That limits the useful range of number types to 15 significant digits.

cn:query(query, [options]) -> res,nil,cols | nil,err,errcode,sqlstate

This is a shortcut for combining the send_query call and the first read_result call.

You should always check if the err return value is again in case of success because this method will only call read_result once for you.

cn:prepare(query, [opt]) -> stmt

Prepare a statement. Options can contain:

  • cursor: ‘read_only’, ‘update’, ‘scrollabe’, ‘none’ (default: ‘none’).


Execute a statement. Use cn:read_result() to get the results.


Free statement.


The MySQL server version string.

cn:quote(s) -> s

Quote literal string to be used in queries. Quoting only works if current collation is known (ses collation arg on connect()).

Multiple result set support

For a SQL query that produces multiple result-sets, it is always your duty to check the ‘again’ error message returned by the query, and keep pulling more result sets by calling the read_result() until no ‘again’ error message returned (or some other errors happen).



By default, of all authentication methods, only Old Password Authentication(mysql_old_password) and Secure Password Authentication(mysql_native_password) are suppored.


  • implement the data compression support in the protocol.

Last updated: 5 months ago | Edit on GitHub

Pkg type:Lua
Version: 8e6c42f
Last commit:
Author: Yichun Zhang (agentzh)
License: BSD

Requires: none

Required by: none