Which opening is the longest?

Why bother calling it "chess" anymore if interested in using a database for as much as the first 20 moves or more?

In a vote game, my team uncorked a novelty on move 32 of a Sicilian Najdorf Poisoned Pawn variation once.

You have to use the data base to get out of the data base and then you are not always sure that you fell for a move order trick.  White can generally get out of the data base easily before move 20.  Sometimes Black has to stick to theory to survive.  I would say, in general, the burden is on White to find a novelty.

You don't get it. Those who play, using a database, should stick the database in their ear. That's what I'm saying.

wow can you give a link to  that game.

I don't know if it qualifies for a 'wow,' but here it is: Team Italia vs. Team Canada.

In the middlegame it's called theory.

I found another one as long, a different move for Black in the very same variation.  Did this somewhat scientifically on the cygwin command line, as you can see there are no results matching '19.' (and the second search more specifically searchs for variations 18 moves deep where Black has played a move) in the Arena eco codes text file I used as my source:

root@W7-Desktop /cygdrive/c/opt/chess/engines
$ cat arena_3.0/ecocodes9.txt | grep '19\.'

root@W7-Desktop /cygdrive/c/opt/chess/engines
$ cat arena_3.0/ecocodes9.txt | egrep '18\.\w+\s\w+'

{C89   Spanish: Marshall, Main Line, Classical, Spassky Variation}1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 Nf6 5.O-O Be7 6.Re1 b5 7.Bb3 O-O 8.c3 d5 9.exd5 Nxd5 10.Nxe5 Nxe5 11.Rxe5 c6 12.d4 Bd6 13.Re1 Qh4 14.g3 Qh3 15.Be3 Bg4 16.Qd3 Rae8 17.Nd2 Re6 18.a4 Qh5

{C89   Spanish: Marshall, Main Line, Classical, 18.a4 f5}1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 Nf6 5.O-O Be7 6.Re1 b5 7.Bb3 O-O 8.c3 d5 9.exd5 Nxd5 10.Nxe5 Nxe5 11.Rxe5 c6 12.d4 Bd6 13.Re1 Qh4 14.g3 Qh3 15.Be3 Bg4 16.Qd3 Rae8 17.Nd2 Re6 18.a4 f5

Don't ask me for specific lines as I no longer play these openings, but I can tell you that I've definite seen lines of the Classical King's Indian w/ 9.Ne1 go into the upper-20s or low 30s routinely.  Another is the 6.Bg5 lines of the Najdorf Sicilian, which there is some line that goes minimum 25 moves deep.  I seem to recall a White Rook getting to g7 for some reason.

Yes there are plenty of variations that go 30+ moves deep in terms of published analysis.  But it seems apparent from the OP's partial answer to their own question, that they were interested in the longest categorized opening with respect to their ECO codes and generally accepted sub-variations thereof.

I'm not sure what the longest opening is, but this is the longest one I know. It's a sideline in the najdorf sicilian that I found with the help of an engine after getting sidelined and losing in 8 moves.

u can easily find 30 moves and even more...

For example i played a game against a strong GM, with a line I prepared some months before, up to move 26!

My opponent was out of book at move 16 or before. But what is fantastic is the way he defended a clearly worse position, when I couldn't find the best way to use my advantage.

U could wonder how to remember this? Well, the best way to remember a line is to learn the ideas, and why we play move here, why this order, etc...

I played this line again some months ago, where my opponent didnt know it, and surprised me with a sacrifice at move 22.

One of the nicest feelings in chess is to defeat a player who is all booked up and you're not.  

I've done this on occasion and the booked up player is usually pissed.  

in ruy lopez tchigoroin variation is one of the longests

There was a Ruy Lopez game given in one of my chess books - I think one of the players was Frederick Yates - where the first capture (of a pawn) took place on move 40.

sicilian najdorf, posioned pawn variation?

+1

Ruy López Opening: Morphy Defense, Closed, Pilnik Variation, 9...Na5 10.Bc2. This start at move 10 of white

C89 Ruy Lopez: Marshall, Main line, Spassky Variation
1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 Nf6 5.O-O Be7 6.Re1 b5 7.Bb3 O-O 8.c3 d5 9.exd5 Nxd5 10.Nxe5 Nxe5 11.Rxe5 c6 12.d4 Bd6 13.Re1 Qh4 14.g3 Qh3 15.Be3 Bg4 16.Qd3 Rae8 17.Nd2 Re6 18.a4 Qh5

It's some variation of KID or KIA