Github user viirya commented on a diff in the pull request:
https://github.com/apache/spark/pull/15090#discussion_r79327748
--- Diff:
sql/core/src/test/scala/org/apache/spark/sql/StatisticsSuite.scala ---
@@ -101,4 +101,47 @@ class StatisticsSuite extends QueryTest with
SharedSQLContext {
checkTableStats(tableName, expectedRowCount = Some(2))
}
}
+
+ test("test column-level statistics for data source table created in
InMemoryCatalog") {
+ def checkColStats(colStats: BasicColStats, expectedColStats:
BasicColStats): Unit = {
+ assert(colStats.dataType == expectedColStats.dataType)
+ assert(colStats.numNulls == expectedColStats.numNulls)
+ assert(colStats.max == expectedColStats.max)
+ assert(colStats.min == expectedColStats.min)
+ if (expectedColStats.ndv.isDefined) {
+ // ndv is an approximate value, so we just make sure we have the
value
+ assert(colStats.ndv.get >= 0)
--- End diff --
It should be:
1. estimate column statistics for several times.
2. calculate mean and standard deviation of ndv for the multiple statistics.
3. check if the real ndv value is within (mean + 3 * sd, mean - 3 * sd).
Please correct me if it is wrong.
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