[GitHub] rdblue edited a comment on issue #75: Add startsWith predicate

[GitBox <gi...@apache.org>]

rdblue edited a comment on issue #75: Add startsWith predicate 
URL: https://github.com/apache/incubator-iceberg/pull/75#issuecomment-453874634
 
 
   @renato2099, inclusive projection happens in the `Transform.project` method. You'll need to update any `Transform` that can project a `startsWith` predicate. That is any transform that can handle strings.
   
   Projection takes a predicate on data values (e.g. `startsWith(str, "aa")`) and returns a predicate that accepts partition values. The translation isn't perfect, so there are two types: inclusive and strict, that make different guarantees.
   
   For example, when you search for `ts > '2019-01-01T00:00:00'`, that's a predicate on data values (the `ts` column).  If your table is partitioned by day, Iceberg needs to use that predicate to match the stored partition values, in order to select the files that may contain data that match your query. Iceberg "projects" the predicate using the partition spec for a table. In this case, the transform `day` is used because the spec uses it on the same column, `ts`. That projects the predicate to `ts_day >= '2019-01-01'`, which can be run on the `ts_day` partition values.

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