Custom date logic to extend effective range of date type #39
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used if we want to read parquet files, such as some of the splink_datasets
this allows us to pre-make a ColumnExpression to pass, or more interestingly to pre-process the input data
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Native date types in Clickhouse don't work for dates before 1900. This is fine for most use cases, but occasionally one may be interested in linking data that deals with dates before then - for instance historical census data.
This creates some custom logic to handle dates before then. Specifically:
days_since_epochthat converts a string (in standard ISO-8601 format) into a signed integer representing the number of days since1970-01-01(-ve days meaning days before this)ColumnExpressionto create a transform for parsing a date to an int of this typecll.AbsoluteDateDifferenceLevel,cl.AbsoluteDateDifferenceAtThresholds, andcl.DateOfBirthComparisonthat all use this type under-the-hood, either with a pre-made integer column, or doing the parsing on-the-flyThis is treating dates as being in the proleptic Gregorian calendar.