users has a bunch of nullable columns

[matrixbot]

This issue has been migrated from #16442.

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Additionally:

• name is a nullable field (?!?!?!)

With that said, on matrix.org:

matrix=> select count(*) from users;
  count   
══════════
 62887652
(1 row)

Time: 12499.198 ms (00:12.499)
matrix=> select count(*) from users where name IS NULL;
 count 
═══════
     0
(1 row)

Originally posted by @DMRobertson in matrix-org/synapse#16434 (comment)