You are now a sqlite data analyst, and you are given a database schema as follows:

    【Schema】
    【DB_ID】 codebase_community
【Schema】
# Table: votes
[
(Id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(PostId:INTEGER, Examples: [3, 2, 5]),
(VoteTypeId:INTEGER, Examples: [2, 5, 3]),
(CreationDate:DATE, Examples: [2010-07-19]),
(UserId:INTEGER, Examples: [58, 6, 66]),
(BountyAmount:INTEGER, Examples: [50, 25, 0])
]
# Table: tags
[
(Id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(TagName:TEXT, Examples: [bayesian, prior, elicitation]),
(Count:INTEGER, Examples: [1342, 168, 6]),
(ExcerptPostId:INTEGER, Examples: [20258, 62158, 67815]),
(WikiPostId:INTEGER, Examples: [20257, 62157, 67814])
]
# Table: posts
[
(Id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(PostTypeId:INTEGER, Examples: [1, 2, 7]),
(AcceptedAnswerId:INTEGER, Examples: [15, 59, 5]),
(CreaionDate:DATETIME, Examples: [2010-07-19 19:12:12]),
(Score:INTEGER, Examples: [23, 22, 54]),
(ViewCount:INTEGER, Examples: [1278, 8198, 3613]),
(Body:TEXT),
(OwnerUserId:INTEGER, Examples: [8, 24, 18]),
(LasActivityDate:DATETIME, Examples: [2010-09-15 21:08:26]),
(Title:TEXT),
(Tags:TEXT, Examples: [<bayesian><prior><elicitation>]),
(AnswerCount:INTEGER, Examples: [5, 7, 19]),
(CommentCount:INTEGER, Examples: [1, 4, 2]),
(FavoriteCount:INTEGER, Examples: [14, 8, 36]),
(LastEditorUserId:INTEGER, Examples: [88, 183, 23]),
(LastEditDate:DATETIME, Examples: [2010-08-07 17:56:44]),
(CommunityOwnedDate:DATETIME, Examples: [2010-07-19 19:13:28]),
(ParentId:INTEGER, Examples: [3, 7, 6]),
(ClosedDate:DATETIME, Examples: [2010-07-19 20:19:46]),
(OwnerDisplayName:TEXT, Examples: [user28, user209, Michael Bishop]),
(LastEditorDisplayName:TEXT, Examples: [user28, user10525, sjcockell])
]
# Table: users
[
(Id:INTEGER, Primary Key, Examples: [-1, 2, 3]),
(Reputation:INTEGER, Examples: [1, 101, 6792]),
(CreationDate:DATETIME, Examples: [2010-07-19 06:55:26]),
(DisplayName:TEXT, Examples: [Community, Geoff Dalgas, Jarrod Dixon]),
(LastAccessDate:DATETIME, Examples: [2010-07-19 06:55:26]),
(WebsiteUrl:TEXT),
(Location:TEXT, Examples: [on the server farm, Corvallis, OR, New York, NY]),
(AboutMe:TEXT),
(Views:INTEGER, Examples: [0, 25, 22]),
(UpVotes:INTEGER, Examples: [5007, 3, 19]),
(DownVotes:INTEGER, Examples: [1920, 0, 5]),
(AccountId:INTEGER, Examples: [-1, 2, 3]),
(Age:INTEGER, Examples: [37, 35, 28]),
(ProfileImageUrl:TEXT)
]
# Table: postHistory
[
(Id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(PostHistoryTypeId:INTEGER, Examples: [2, 1, 3]),
(PostId:INTEGER, Examples: [1, 2, 3]),
(RevisionGUID:TEXT, Examples: [e58bf7fd-e60f-4c58-a6e4-dfc91cf98a69]),
(CreationDate:DATETIME, Examples: [2010-07-19 19:12:12]),
(UserId:INTEGER, Examples: [8, 24, 18]),
(Text:TEXT),
(Comment:TEXT),
(UserDisplayName:TEXT, Examples: [user28, user209, Michael Bishop])
]
# Table: comments
[
(Id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(PostId:INTEGER, Examples: [3, 5, 9]),
(Score:INTEGER, Examples: [5, 0, 11]),
(Text:TEXT),
(CreationDate:DATETIME, Examples: [2010-07-19 19:15:52]),
(UserId:INTEGER, Examples: [13, 37, 5]),
(UserDisplayName:TEXT, Examples: [user28, Statprof, jjgibaja])
]
# Table: postLinks
[
(Id:INTEGER, Primary Key, Examples: [108, 145, 217]),
(CreationDate:DATETIME, Examples: [2010-07-21 14:47:33]),
(PostId:INTEGER, Examples: [395, 548, 375]),
(RelatedPostId:INTEGER, Examples: [173, 539, 30]),
(LinkTypeId:INTEGER, Examples: [1, 3])
]
# Table: badges
[
(Id:INTEGER, Primary Key, Examples: [1, 2, 3]),
(UserId:INTEGER, Examples: [5, 6, 8]),
(Name:TEXT, Examples: [Teacher, Student, Editor]),
(Date:DATETIME, Examples: [2010-07-19 19:39:07])
]
【Foreign keys】
votes.PostId=posts.Id
votes.UserId=users.Id
tags.ExcerptPostId=posts.Id
posts.LastEditorUserId=users.Id
posts.OwnerUserId=users.Id
posts.ParentId=posts.Id
postHistory.PostId=posts.Id
postHistory.UserId=users.Id
comments.PostId=posts.Id
comments.UserId=users.Id
postLinks.PostId=posts.Id
postLinks.RelatedPostId=posts.Id
badges.UserId=users.Id

    【Question】
    Among products comments with 0 score, what is the total number of users ages 40 years old?

    【Evidence】
    

    Please read and understand the database schema carefully, and generate an executable SQL based on the user's question and evidence. 

SQL: SELECT COUNT(DISTINCT T1.id) FROM comments AS T1 INNER JOIN users AS T2 ON T1.UserId = T2.Id WHERE T1.Score = 0 AND T2.Age = 40