Bug Report

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1. Minimal reproduce step (Required)

Filter operator should always return constant 1 column for filter column, but in current implementation, it may not be true if a block with all rows be kept:

I believe it is just a typo because the comments shows "Replace the column with the filter by a constant."

Filter not return constant column for filter column may make sort spill crash because in sort operator, it will remove constant column:

If some block returned by filter operator contants constant column while others does not contain constant column, the block in sorted_blocks will have different schemas, which will cause a series of troubles, the worst case is make TiFlash crash.

2. What did you expect to see? (Required)

3. What did you see instead (Required)

4. What is your TiFlash version? (Required)