Question

I have a vessel tracking database schema with the following table for the schdual

CREATE TABLE IF NOT EXISTS `string_ports` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `string_id` int(10) NOT NULL,
  `port_id` int(11) NOT NULL,
  `port_order` int(10) NOT NULL,
  `arriv_date` datetime NOT NULL,
  `dep_date` datetime NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM  DEFAULT CHARSET=latin1 CHECKSUM=1 DELAY_KEY_WRITE=1 AUTO_INCREMENT=1 ;

the string_id is the id of the line for example I have 3 lines
Line 1 goes from port A to B to C to D
Line 2 goes from port A to C to D
Line 3 goes from port A to Z to B

I need a SQL query the if I want to search for lines going from port A to port C either directly or passing by other ports

so the SQL should say select strings from the string_ports where port C port_order > port A port order and they are on the same string

how can I write that SQl ??

Answer 1

Give this a try:

select a.`string_id`
from `string_ports` as a
inner join `string_ports` as c
on a.`string_id` = c.`string_id`
and a.`port_id` = 1 --whatever port_id A is
and c.`port_id` = 3 --whatever port_id C is
and a.`port_order` < c.`port_order`