I need to clarify some doubts about the career of a cricketer.
If a player played for Under-19 international matches, will they be added in his ODI career?
If a player played any domestic matches like IPL, CLT20, will they be added in his Twenty20 career?
What is the difference between Twenty20 career and T20I career?
What are First-class, List-A matches? When these matches were played?
One day internationals are defined by the ICC as occurring between senior teams representing their country in ICC sanctioned matches. Under 19s cricket is clearly a very different standard and it would obviously make no sense to roll these games into career ODI statistics.
Likewise, T20I cricket must be senior teams representing their country, so IPL, BBL or even CLT20 does not count as T20I nor would any U19 games.
The term 'First class' cricket refers to long form, non-limited overs cricket played at the highest standard within a country. This means for instance Ranji Trophy matches in India, English country cricket 4 day games and Sheffield Shield games in Australia. Club cricket does not count as 'First Class' because it is not the highest standard domestic cricket. Essentially First Class cricket it the closest thing to Test Cricket, but typically is played over 4 rather than 5 days however 3 day matches can still qualify as first class cricket. See here for more detail.
The term 'List A' refers to domestic limited overs cricket, again played at the highest standard within that country. This includes various competitions in which the games are between 40-60 overs. See the wiki page for more info on what does and doesn't count as List A.
Domestic T20 cricket includes games played in leagues such as the IPL, BBL etc. As far as I know the ICC has not yet codified exactly what constitutes official T20 records, i.e. presumably a Sydney park cricket T20 comp does not count, but where is the line drawn? In practice cricket stats sites use only stats from the premier T20 league played in a given country. But again, these career stats are different to a players T20I stats.
To see this in action, have a look at the stats as recorded by cricketarchive.com (which is officially endorsed by the ICC) for Mike Hussey. You can see clearly that the domestic records for First Class cricket are separated from Test cricket, ODIs are separated from List A and T20I is separated from T20 domestic. In addition, his under 19 records are again listed separately from his senior cricket records.
The only controversy in this area is the 6 day 'super test' and 3 one day matches played in the early 2000s between Australia and a World team. Some people don't believe these matches should count towards career stats for Test matches and ODIs respectively however the ICC has declared that they do count. The World Series rebel games played in the 70s also are not counted in career stats of players because these were not sanctioned by the MCC (the body that ran cricket before the ICC existed).
I have tried to give you answers one by one.
If a player played for under19 international matches,will they be added in his odi career?
I couldn't find any official source where it is mentioned that Under-19 Cricket's stats count or not towards his international career. But from any player's career statistics we can easily find that Under-19 Cricket's stats do not count in international matches.
For example: Have a look at Cheteshwar Pujara's Career page. He was the captain of Under-19 world cup team for 2006. But looking at his career statistics after his debut in ODI vs Zimbabwe it is clear that Under-19 Cricket's stats don't count in international matches.
Another example is Unmukt Chand. He was the captain of the winning team of Under-19 WC 2012. Looking at his career page before his ODI debut there is no record for his ODI career.
If a player played any domestic matches like IPL,CLT20,will they be added in his Twenty20 career?
Yes. Have a look at Jaydev Unadkat's career page. See his Twenty20 career debut match. It is KKR v KXIP at Kolkata, Apr 4, 2010. So it is clearly stats that IPL as well as CLT20 will be added in player's Twenty20 career.
What is the difference between Twenty20 career and T20i career?
Twenty20 includes all 20-20 matches while T20I includes only international T20 matches.
What are first-class,List-A matches?
From Wikipedia
First-class cricket is a class of the game of cricket comprising matches of three or more days' scheduled duration between two sides of eleven players each, officially adjudged to be first-class by virtue of the standard of the competing teams. Matches must allow for the teams to play two innings each.
So all matches scheduled for more than two days' and allowing four innings (two innings each) are considered as First-class cricket matches. This also include Test matches (i.e. international) as well.
List A cricket is a classification of the limited-overs (one-day) form of the sport of cricket. Much as domestic first-class cricket is the level below international Test match cricket, so List A cricket is the domestic level of one-day cricket below One Day International.
List A matches means limited overs cricket match (and not Twenty20) played in one day. This includes ODI as well.
when these matches were played?
I really can't understand this question. Such matches (First-class and List A) are constantly played in domestic and international level. For e.g. Ranji Trophy is a First-class matches trophy. Which is played every year since 1934. Or Vijay Hazare Trophy is a domestic matches trophy which is also played every year.
Twenty20 -- Domestic matches like played for the State team, county, IPL team etc.
T20I -- International Twenty20 matches
First class -- Domestic Test matches
List A -- Domestic one day matches
