Implement count distinct for dictionary arrays #256
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Which issue does this PR close?
Closes #249
Rationale for this change
I have dictionary encoded data that I want to be able to compute distinct counts
What changes are included in this PR?
This implementation has the the basic "get it working" version. A more optimized implementation (e.g. only looking at the dictionary contents) is left for a subsequent PR and #258 tracks better performance
Are there any user-facing changes?
queries like
select count(distinct tag_col) from ...are now supported whentag_colis a dictionary encoded column