From 01e8ffaba74523449920fa85d1c0334c6d3039d7 Mon Sep 17 00:00:00 2001
From: Colin Dellow <cldellow@gmail.com>
Date: Fri, 16 Mar 2018 16:30:05 -0400
Subject: [PATCH] Row group filtering for double/float

---
 README.md                 | 31 +++++++++++++++++---
 parquet/parquet_cursor.cc | 62 ++++++++++++++++++++++++++++++++++++++-
 2 files changed, 88 insertions(+), 5 deletions(-)

diff --git a/README.md b/README.md
index e4641d4..50b3399 100644
--- a/README.md
+++ b/README.md
@@ -33,13 +33,36 @@ sqlite> SELECT * FROM demo;
 
 ## Supported features
 
-### Index
+### Row group filtering
 
-Only full table scans are supported.
+Row group filtering is supported for strings and numerics so long as the SQLite
+type matches the Parquet type.
+
+e.g. if you have a column `foo` that is an INT32, this query will skip row groups whose
+statistics prove that it does not contain relevant rows:
+
+```
+SELECT * FROM tbl WHERE foo = 123;
+```
+
+but this query will devolve to a table scan:
+
+```
+SELECT * FROM tbl WHERE foo = '123';
+```
+
+This is laziness on my part and could be fixed without too much effort.
+
+### Row filtering
+
+For common constraints, the row is checked to see if it satisfies the query's
+constraints before returning control to SQLite's virtual machine. This minimizes
+the number of allocations performed when many rows are filtered out by
+the user's criteria.
 
 ### Types
 
-These types are supported:
+These Parquet types are supported:
 
 * INT96 timestamps (exposed as milliseconds since the epoch)
 * INT8/INT16/INT32/INT64
@@ -49,7 +72,7 @@ These types are supported:
 * DOUBLE
 * Variable- and fixed-length byte arrays
 
-These are not supported:
+These are not currently supported:
 
 * UINT8/UINT16/UINT32/UINT64
 * DECIMAL
diff --git a/parquet/parquet_cursor.cc b/parquet/parquet_cursor.cc
index 11ab67e..3db8d3e 100644
--- a/parquet/parquet_cursor.cc
+++ b/parquet/parquet_cursor.cc
@@ -160,8 +160,68 @@ bool ParquetCursor::currentRowGroupSatisfiesIntegerFilter(Constraint& constraint
   return true;
 }
 
-bool ParquetCursor::currentRowGroupSatisfiesDoubleFilter(Constraint& constraint, std::shared_ptr<parquet::RowGroupStatistics> stats) {
+bool ParquetCursor::currentRowGroupSatisfiesDoubleFilter(Constraint& constraint, std::shared_ptr<parquet::RowGroupStatistics> _stats) {
+  if(!_stats->HasMinMax()) {
+    return true;
+  }
+
+  if(constraint.type != Double) {
+    return true;
+  }
+
+  int column = constraint.column;
+
+  double min = std::numeric_limits<double>::min();
+  double max = std::numeric_limits<double>::max();
+  parquet::Type::type pqType = types[column];
+
+  if(pqType == parquet::Type::DOUBLE) {
+    parquet::TypedRowGroupStatistics<parquet::DataType<parquet::Type::DOUBLE>>* stats =
+      (parquet::TypedRowGroupStatistics<parquet::DataType<parquet::Type::DOUBLE>>*)_stats.get();
+
+    min = stats->min();
+    max = stats->max();
+  } else if(pqType == parquet::Type::FLOAT) {
+    parquet::TypedRowGroupStatistics<parquet::DataType<parquet::Type::FLOAT>>* stats =
+      (parquet::TypedRowGroupStatistics<parquet::DataType<parquet::Type::FLOAT>>*)_stats.get();
+
+    min = stats->min();
+    max = stats->max();
+  } else {
+    // Should be impossible to get here as we should have forbidden this at
+    // CREATE time -- maybe file changed underneath us?
+    std::ostringstream ss;
+    ss << __FILE__ << ":" << __LINE__ << ": currentRowGroupSatisfiesIntegerFilter called on unsupported type: " <<
+      parquet::TypeToString(pqType);
+    throw std::invalid_argument(ss.str());
+  }
+
+  const double value = constraint.doubleValue;
+//  printf("min=%s [%d], max=%s [%d], target=%s\n", minStr.data(), min.len, maxStr.data(), max.len, str.data());
+
+  switch(constraint.op) {
+    case Is:
+    case Equal:
+      return value >= min && value <= max;
+    case GreaterThanOrEqual:
+      return max >= value;
+    case GreaterThan:
+      return max > value;
+    case LessThan:
+      return min < value;
+    case LessThanOrEqual:
+      return min <= value;
+    case IsNot:
+    case NotEqual:
+      // If min == max == str, we can skip this.
+      return !(min == max && value == min);
+    case Like:
+    default:
+      return true;
+  }
+
   return true;
+
 }
 
 bool ParquetCursor::currentRowSatisfiesTextFilter(Constraint& constraint) {