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MySQL client protocol in Lua

local mysql = require'mysql'

MySQL client protocol in Lua. Ripped from OpenResty, modified to work with sock (but you can bring your own I/O), added prepared statements, better interpretation of field metadata (consistent with sqlpp, schema and x-widgets), and other minor changes.


local mysql = require'mysql'

   host = '',
   port = 3306,
   user = 'bar',
   password = 'baz',
   db = '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).
  • db: the database to set as current database (optional).
  • charset: the character set used for the connection (required, see below).
  • collation: the collation used for the connection (required, see below). * if only charset is given, the default collation for the charset is set automatically. * if collation is given, charset is set automatically and must not be supplied.
  • 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() -> true | nil,err

Closes the current mysql connection and returns the status.

cn:closed() -> true | false

Check if the connection was closed.

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
    • NOTE: unless you set null_value, the rows in compact mode will be sparse arrays so ipairs(row) and #row won’t work on them (but #cols will).
  • to_array = true – return an array of values for single-column results.
  • null_value = val – value to use for null (defaults to nil).
  • field_attrs = {name -> attr} – extra field attributes. It can also be a function which will be called as field_attrs(cn, fields, opt) as soon as field metadata is received but before rows are received (so you can even set a custom mysql_to_lua for particular fields).

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: Decimals with up to 15 digits of precision and 64 bit integers are converted to Lua numbers by default. That limits the useful range of integer types to 15 significant digits. If you have other needs, provide your own to_lua (which you can set at module or connection level, per query in field_attrs, or in a schema column definition with the mysql_to_lua attribute).

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.

mysql.esc_utf8(s) -> s

Escape string to be used inside SQL string literals. Only works on connections for which the charset is ASCII or an ASCII superset (ascii, utf8).

cn:esc(s) -> s

Escape string to be used inside SQL string literals.

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: 21 months ago | Edit on GitHub

Pkg type:Lua+ffi
Version: ae43275
Last commit:
Author: Cosmin Apreutesei
License: Public Domain

Requires: errors  glue  luajit  sha1 

Required by: sqlpp  webb  x-widgets