Merge pull request #840 from katzyn/median

Add MEDIAN aggregate

h2/src/main/org/h2/expression/Aggregate.java

@@ -123,7 +123,12 @@ public class Aggregate extends Expression {
         /**
          * The aggregate type for HISTOGRAM(expression).
          */
-        HISTOGRAM
+        HISTOGRAM,
+
+        /**
+         * The aggregate type for MEDIAN(expression).
+         */
+        MEDIAN
     }
 
     private static final HashMap<String, AggregateType> AGGREGATES = new HashMap<>(24);
@@ -187,6 +192,7 @@ public class Aggregate extends Expression {
         addAggregate("HISTOGRAM", AggregateType.HISTOGRAM);
         addAggregate("BIT_OR", AggregateType.BIT_OR);
         addAggregate("BIT_AND", AggregateType.BIT_AND);
+        addAggregate("MEDIAN", AggregateType.MEDIAN);
     }
 
     private static void addAggregate(String name, AggregateType type) {
@@ -287,7 +293,7 @@ public class Aggregate extends Expression {
                 Table table = select.getTopTableFilter().getTable();
                 return ValueLong.get(table.getRowCount(session));
             case MIN:
-            case MAX:
+            case MAX: {
                 boolean first = type == AggregateType.MIN;
                 Index index = getMinMaxColumnIndex();
                 int sortType = index.getIndexColumns()[0].sortType;
@@ -303,6 +309,10 @@ public class Aggregate extends Expression {
                     v = row.getValue(index.getColumns()[0].getColumnId());
                 }
                 return v;
+            }
+            case MEDIAN: {
+                return AggregateDataMedian.getFromIndex(session, on, dataType);
+            }
             default:
                 DbException.throwInternalError("type=" + type);
             }
@@ -434,6 +444,7 @@ public class Aggregate extends Expression {
             break;
         case MIN:
         case MAX:
+        case MEDIAN:
             break;
         case STDDEV_POP:
         case STDDEV_SAMP:
@@ -568,6 +579,9 @@ public class Aggregate extends Expression {
         case BIT_OR:
             text = "BIT_OR";
             break;
+        case MEDIAN:
+            text = "MEDIAN";
+            break;
         default:
             throw DbException.throwInternalError("type=" + type);
         }
@@ -606,6 +620,11 @@ public class Aggregate extends Expression {
             case MAX:
                 Index index = getMinMaxColumnIndex();
                 return index != null;
+            case MEDIAN:
+                if (distinct) {
+                    return false;
+                }
+                return AggregateDataMedian.getMedianColumnIndex(on) != null;
             default:
                 return false;
             }

h2/src/main/org/h2/expression/AggregateData.java

@@ -31,6 +31,8 @@ abstract class AggregateData {
             return new AggregateDataCount();
         } else if (aggregateType == AggregateType.HISTOGRAM) {
             return new AggregateDataHistogram();
+        } else if (aggregateType == AggregateType.MEDIAN) {
+            return new AggregateDataMedian();
         } else {
             return new AggregateDataDefault(aggregateType);
         }

h2/src/main/org/h2/expression/AggregateDataMedian.java

+/*
+ * Copyright 2004-2018 H2 Group. Multiple-Licensed under the MPL 2.0,
+ * and the EPL 1.0 (http://h2database.com/html/license.html).
+ * Initial Developer: H2 Group
+ */
+package org.h2.expression;
+
+import java.math.BigDecimal;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Comparator;
+import java.util.HashSet;
+
+import org.h2.engine.Database;
+import org.h2.engine.Session;
+import org.h2.index.Cursor;
+import org.h2.index.Index;
+import org.h2.result.SearchRow;
+import org.h2.result.SortOrder;
+import org.h2.table.Column;
+import org.h2.table.IndexColumn;
+import org.h2.table.Table;
+import org.h2.table.TableFilter;
+import org.h2.util.DateTimeUtils;
+import org.h2.value.CompareMode;
+import org.h2.value.Value;
+import org.h2.value.ValueDate;
+import org.h2.value.ValueDecimal;
+import org.h2.value.ValueDouble;
+import org.h2.value.ValueFloat;
+import org.h2.value.ValueInt;
+import org.h2.value.ValueLong;
+import org.h2.value.ValueNull;
+import org.h2.value.ValueTime;
+import org.h2.value.ValueTimestamp;
+import org.h2.value.ValueTimestampTimeZone;
+
+/**
+ * Data stored while calculating a MEDIAN aggregate.
+ */
+class AggregateDataMedian extends AggregateData {
+    private Collection<Value> values;
+
+    static Index getMedianColumnIndex(Expression on) {
+        if (on instanceof ExpressionColumn) {
+            ExpressionColumn col = (ExpressionColumn) on;
+            Column column = col.getColumn();
+            TableFilter filter = col.getTableFilter();
+            if (filter != null) {
+                Table table = filter.getTable();
+                ArrayList<Index> indexes = table.getIndexes();
+                Index result = null;
+                if (indexes != null) {
+                    for (int i = 1, size = indexes.size(); i < size; i++) {
+                        Index index = indexes.get(i);
+                        if (!index.canFindNext()) {
+                            continue;
+                        }
+                        if (!index.isFirstColumn(column)) {
+                            continue;
+                        }
+                        IndexColumn ic = index.getIndexColumns()[0];
+                        if (column.isNullable()) {
+                            int sortType = ic.sortType;
+                            // Nulls last is not supported
+                            if ((sortType & SortOrder.NULLS_LAST) != 0)
+                                continue;
+                            // Descending without nulls first is not supported
+                            if ((sortType & SortOrder.DESCENDING) != 0 && (sortType & SortOrder.NULLS_FIRST) == 0) {
+                                continue;
+                            }
+                        }
+                        if (result == null || result.getColumns().length > index.getColumns().length) {
+                            result = index;
+                        }
+                    }
+                }
+                return result;
+            }
+        }
+        return null;
+    }
+
+    static Value getFromIndex(Session session, Expression on, int dataType) {
+        Index index = getMedianColumnIndex(on);
+        long count = index.getRowCount(session);
+        if (count == 0) {
+            return ValueNull.INSTANCE;
+        }
+        Cursor cursor = index.find(session, null, null);
+        cursor.next();
+        // Skip nulls
+        SearchRow row;
+        while (count > 0) {
+            row = cursor.getSearchRow();
+            if (row == null) {
+                return ValueNull.INSTANCE;
+            }
+            if (row.getValue(index.getColumns()[0].getColumnId()) == ValueNull.INSTANCE) {
+                count--;
+                cursor.next();
+            } else
+                break;
+        }
+        if (count == 0) {
+            return ValueNull.INSTANCE;
+        }
+        long skip = (count - 1) / 2;
+        for (int i = 0; i < skip; i++) {
+            cursor.next();
+        }
+        row = cursor.getSearchRow();
+        Value v;
+        if (row == null) {
+            v = ValueNull.INSTANCE;
+        } else {
+            v = row.getValue(index.getColumns()[0].getColumnId());
+        }
+        if ((count & 1) == 0) {
+            cursor.next();
+            row = cursor.getSearchRow();
+            if (row == null) {
+                return v;
+            }
+            Value v2 = row.getValue(index.getColumns()[0].getColumnId());
+            return getMedian(v, v2, dataType, session.getDatabase().getCompareMode());
+        }
+        return v;
+    }
+
+    @Override
+    void add(Database database, int dataType, boolean distinct, Value v) {
+        if (v == ValueNull.INSTANCE) {
+            return;
+        }
+        Collection<Value> c = values;
+        if (c == null) {
+            values = c = distinct ? new HashSet<Value>() : new ArrayList<Value>();
+        }
+        c.add(v);
+    }
+
+    @Override
+    Value getValue(Database database, int dataType, boolean distinct) {
+        Collection<Value> c = values;
+        if (c == null) {
+            return ValueNull.INSTANCE;
+        }
+        if (distinct && c instanceof ArrayList) {
+            c = new HashSet<>(c);
+        }
+        Value[] a = c.toArray(new Value[0]);
+        final CompareMode mode = database.getCompareMode();
+        Arrays.sort(a, new Comparator<Value>() {
+            @Override
+            public int compare(Value o1, Value o2) {
+                return o1.compareTo(o2, mode);
+            }
+        });
+        int len = a.length;
+        int idx = len / 2;
+        Value v1 = a[idx];
+        if ((len & 1) == 1) {
+            return v1.convertTo(dataType);
+        }
+        return getMedian(a[idx - 1], v1, dataType, mode);
+    }
+
+    static Value getMedian(Value v0, Value v1, int dataType, CompareMode mode) {
+        if (v0.compareTo(v1, mode) == 0) {
+            return v0.convertTo(dataType);
+        }
+        switch (dataType) {
+        case Value.BYTE:
+        case Value.SHORT:
+        case Value.INT:
+            return ValueInt.get((v0.getInt() + v1.getInt()) / 2).convertTo(dataType);
+        case Value.LONG:
+            return ValueLong.get((v0.getLong() + v1.getLong()) / 2);
+        case Value.DECIMAL:
+            return ValueDecimal.get(v0.getBigDecimal().add(v1.getBigDecimal()).divide(BigDecimal.valueOf(2)));
+        case Value.FLOAT:
+            return ValueFloat.get((v0.getFloat() + v1.getFloat()) / 2);
+        case Value.DOUBLE:
+            return ValueDouble.get((v0.getFloat() + v1.getDouble()) / 2);
+        case Value.TIME: {
+            return ValueTime.fromMillis((v0.getTime().getTime() + v1.getTime().getTime()) / 2);
+        }
+        case Value.DATE: {
+            ValueDate d0 = (ValueDate) v0.convertTo(Value.DATE), d1 = (ValueDate) v1.convertTo(Value.DATE);
+            return ValueDate.fromDateValue(
+                    DateTimeUtils.dateValueFromAbsoluteDay((DateTimeUtils.absoluteDayFromDateValue(d0.getDateValue())
+                            + DateTimeUtils.absoluteDayFromDateValue(d1.getDateValue())) / 2));
+        }
+        case Value.TIMESTAMP: {
+            ValueTimestamp ts0 = (ValueTimestamp) v0.convertTo(Value.TIMESTAMP),
+                    ts1 = (ValueTimestamp) v1.convertTo(Value.TIMESTAMP);
+            long dateSum = DateTimeUtils.absoluteDayFromDateValue(ts0.getDateValue())
+                    + DateTimeUtils.absoluteDayFromDateValue(ts1.getDateValue());
+            long nanos = (ts0.getTimeNanos() + ts1.getTimeNanos()) / 2;
+            if ((dateSum & 1) != 0) {
+                nanos += DateTimeUtils.NANOS_PER_DAY / 2;
+                if (nanos >= DateTimeUtils.NANOS_PER_DAY) {
+                    nanos -= DateTimeUtils.NANOS_PER_DAY;
+                    dateSum++;
+                }
+            }
+            return ValueTimestamp.fromDateValueAndNanos(DateTimeUtils.dateValueFromAbsoluteDay(dateSum / 2), nanos);
+        }
+        case Value.TIMESTAMP_TZ: {
+            ValueTimestampTimeZone ts0 = (ValueTimestampTimeZone) v0.convertTo(Value.TIMESTAMP_TZ),
+                    ts1 = (ValueTimestampTimeZone) v1.convertTo(Value.TIMESTAMP_TZ);
+            long dateSum = DateTimeUtils.absoluteDayFromDateValue(ts0.getDateValue())
+                    + DateTimeUtils.absoluteDayFromDateValue(ts1.getDateValue());
+            long nanos = (ts0.getTimeNanos() + ts1.getTimeNanos()) / 2;
+            if ((dateSum & 1) != 0) {
+                nanos += DateTimeUtils.NANOS_PER_DAY / 2;
+                if (nanos >= DateTimeUtils.NANOS_PER_DAY) {
+                    nanos -= DateTimeUtils.NANOS_PER_DAY;
+                    dateSum++;
+                }
+            }
+            return ValueTimestampTimeZone.fromDateValueAndNanos(DateTimeUtils.dateValueFromAbsoluteDay(dateSum / 2),
+                    nanos, (short) ((ts0.getTimeZoneOffsetMins() + ts1.getTimeZoneOffsetMins()) / 2));
+        }
+        default:
+            // Just return first
+            return v0.convertTo(dataType);
+        }
+    }
+
+}

h2/src/main/org/h2/util/DateTimeUtils.java

@@ -42,7 +42,10 @@ public class DateTimeUtils {
      */
     public static final TimeZone UTC = TimeZone.getTimeZone("UTC");
 
-    private static final long NANOS_PER_DAY = MILLIS_PER_DAY * 1000000;
+    /**
+     * The number of nanoseconds per day.
+     */
+    public static final long NANOS_PER_DAY = MILLIS_PER_DAY * 1000000;
 
     private static final int SHIFT_YEAR = 9;
     private static final int SHIFT_MONTH = 5;

h2/src/test/org/h2/test/db/TestFunctions.java

@@ -740,12 +740,12 @@ public class TestFunctions extends TestBase implements AggregateFunction {
         deleteDb("functions");
         Connection conn = getConnection("functions");
         Statement stat = conn.createStatement();
-        stat.execute("CREATE AGGREGATE MEDIAN FOR \"" +
+        stat.execute("CREATE AGGREGATE SIMPLE_MEDIAN FOR \"" +
                 MedianStringType.class.getName() + "\"");
-        stat.execute("CREATE AGGREGATE IF NOT EXISTS MEDIAN FOR \"" +
+        stat.execute("CREATE AGGREGATE IF NOT EXISTS SIMPLE_MEDIAN FOR \"" +
                 MedianStringType.class.getName() + "\"");
         ResultSet rs = stat.executeQuery(
-                "SELECT MEDIAN(X) FROM SYSTEM_RANGE(1, 9)");
+                "SELECT SIMPLE_MEDIAN(X) FROM SYSTEM_RANGE(1, 9)");
         rs.next();
         assertEquals("5", rs.getString(1));
         conn.close();
@@ -756,22 +756,22 @@ public class TestFunctions extends TestBase implements AggregateFunction {
 
         conn = getConnection("functions");
         stat = conn.createStatement();
-        stat.executeQuery("SELECT MEDIAN(X) FROM SYSTEM_RANGE(1, 9)");
+        stat.executeQuery("SELECT SIMPLE_MEDIAN(X) FROM SYSTEM_RANGE(1, 9)");
         DatabaseMetaData meta = conn.getMetaData();
-        rs = meta.getProcedures(null, null, "MEDIAN");
+        rs = meta.getProcedures(null, null, "SIMPLE_MEDIAN");
         assertTrue(rs.next());
         assertFalse(rs.next());
         rs = stat.executeQuery("SCRIPT");
         boolean found = false;
         while (rs.next()) {
             String sql = rs.getString(1);
-            if (sql.contains("MEDIAN")) {
+            if (sql.contains("SIMPLE_MEDIAN")) {
                 found = true;
             }
         }
         assertTrue(found);
-        stat.execute("DROP AGGREGATE MEDIAN");
-        stat.execute("DROP AGGREGATE IF EXISTS MEDIAN");
+        stat.execute("DROP AGGREGATE SIMPLE_MEDIAN");
+        stat.execute("DROP AGGREGATE IF EXISTS SIMPLE_MEDIAN");
         conn.close();
     }
 
@@ -779,12 +779,12 @@ public class TestFunctions extends TestBase implements AggregateFunction {
         deleteDb("functions");
         Connection conn = getConnection("functions");
         Statement stat = conn.createStatement();
-        stat.execute("CREATE AGGREGATE MEDIAN FOR \"" +
+        stat.execute("CREATE AGGREGATE SIMPLE_MEDIAN FOR \"" +
                 MedianString.class.getName() + "\"");
-        stat.execute("CREATE AGGREGATE IF NOT EXISTS MEDIAN FOR \"" +
+        stat.execute("CREATE AGGREGATE IF NOT EXISTS SIMPLE_MEDIAN FOR \"" +
                 MedianString.class.getName() + "\"");
         ResultSet rs = stat.executeQuery(
-                "SELECT MEDIAN(X) FROM SYSTEM_RANGE(1, 9)");
+                "SELECT SIMPLE_MEDIAN(X) FROM SYSTEM_RANGE(1, 9)");
         rs.next();
         assertEquals("5", rs.getString(1));
         conn.close();
@@ -795,22 +795,22 @@ public class TestFunctions extends TestBase implements AggregateFunction {
 
         conn = getConnection("functions");
         stat = conn.createStatement();
-        stat.executeQuery("SELECT MEDIAN(X) FROM SYSTEM_RANGE(1, 9)");
+        stat.executeQuery("SELECT SIMPLE_MEDIAN(X) FROM SYSTEM_RANGE(1, 9)");
         DatabaseMetaData meta = conn.getMetaData();
-        rs = meta.getProcedures(null, null, "MEDIAN");
+        rs = meta.getProcedures(null, null, "SIMPLE_MEDIAN");
         assertTrue(rs.next());
         assertFalse(rs.next());
         rs = stat.executeQuery("SCRIPT");
         boolean found = false;
         while (rs.next()) {
             String sql = rs.getString(1);
-            if (sql.contains("MEDIAN")) {
+            if (sql.contains("SIMPLE_MEDIAN")) {
                 found = true;
             }
         }
         assertTrue(found);
-        stat.execute("DROP AGGREGATE MEDIAN");
-        stat.execute("DROP AGGREGATE IF EXISTS MEDIAN");
+        stat.execute("DROP AGGREGATE SIMPLE_MEDIAN");
+        stat.execute("DROP AGGREGATE IF EXISTS SIMPLE_MEDIAN");
         conn.close();
     }
 

h2/src/test/org/h2/test/scripts/TestScript.java

@@ -99,7 +99,7 @@ public class TestScript extends TestBase {
             testScript("datatypes/" + s + ".sql");
         }
         for (String s : new String[] { "avg", "bit-and", "bit-or", "count",
-                "group-concat", "max", "min", "selectivity", "stddev-pop",
+                "group-concat", "max", "median", "min", "selectivity", "stddev-pop",
                 "stddev-samp", "sum", "var-pop", "var-samp" }) {
             testScript("functions/aggregate/" + s + ".sql");
         }

h2/src/test/org/h2/test/scripts/functions/aggregate/median.sql

+-- Copyright 2004-2018 H2 Group. Multiple-Licensed under the MPL 2.0,
+-- and the EPL 1.0 (http://h2database.com/html/license.html).
+-- Initial Developer: H2 Group
+--
+
+-- ASC
+create table test(v tinyint);
+> ok
+
+create index test_idx on test(v asc);
+> ok
+
+insert into test values (20), (20), (10);
+> update count: 3
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 20
+
+insert into test values (null);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 20
+
+select median(distinct v) from test;
+> MEDIAN(DISTINCT V)
+> ------------------
+> 15
+
+insert into test values (10);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 15
+
+drop table test;
+> ok
+
+-- ASC NULLS FIRST
+create table test(v tinyint);
+> ok
+
+create index test_idx on test(v asc nulls first);
+> ok
+
+insert into test values (20), (20), (10);
+> update count: 3
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 20
+
+insert into test values (null);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 20
+
+select median(distinct v) from test;
+> MEDIAN(DISTINCT V)
+> ------------------
+> 15
+
+insert into test values (10);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 15
+
+drop table test;
+> ok
+
+-- ASC NULLS LAST
+create table test(v tinyint);
+> ok
+
+create index test_idx on test(v asc nulls last);
+> ok
+
+insert into test values (20), (20), (10);
+> update count: 3
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 20
+
+insert into test values (null);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 20
+
+select median(distinct v) from test;
+> MEDIAN(DISTINCT V)
+> ------------------
+> 15
+
+insert into test values (10);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 15
+
+drop table test;
+> ok
+
+-- DESC
+create table test(v tinyint);
+> ok
+
+create index test_idx on test(v desc);
+> ok
+
+insert into test values (20), (20), (10);
+> update count: 3
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 20
+
+insert into test values (null);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 20
+
+select median(distinct v) from test;
+> MEDIAN(DISTINCT V)
+> ------------------
+> 15
+
+insert into test values (10);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 15
+
+drop table test;
+> ok
+
+-- DESC NULLS FIRST
+create table test(v tinyint);
+> ok
+
+create index test_idx on test(v desc nulls first);
+> ok
+
+insert into test values (20), (20), (10);
+> update count: 3
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 20
+
+insert into test values (null);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 20
+
+select median(distinct v) from test;
+> MEDIAN(DISTINCT V)
+> ------------------
+> 15
+
+insert into test values (10);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 15
+
+drop table test;
+> ok
+
+-- DESC NULLS LAST
+create table test(v tinyint);
+> ok
+
+create index test_idx on test(v desc nulls last);
+> ok
+
+insert into test values (20), (20), (10);
+> update count: 3
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 20
+
+insert into test values (null);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 20
+
+select median(distinct v) from test;
+> MEDIAN(DISTINCT V)
+> ------------------
+> 15
+
+insert into test values (10);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 15
+
+drop table test;
+> ok
+
+create table test(v tinyint);
+> ok
+
+insert into test values (20), (20), (10);
+> update count: 3
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 20
+
+insert into test values (null);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 20
+
+select median(distinct v) from test;
+> MEDIAN(DISTINCT V)
+> ------------------
+> 15
+
+insert into test values (10);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 15
+
+drop table test;
+> ok
+
+create table test(v smallint);
+> ok
+
+insert into test values (20), (20), (10);
+> update count: 3
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 20
+
+insert into test values (null);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 20
+
+select median(distinct v) from test;
+> MEDIAN(DISTINCT V)
+> ------------------
+> 15
+
+insert into test values (10);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 15
+
+drop table test;
+> ok
+
+create table test(v int);
+> ok
+
+insert into test values (20), (20), (10);
+> update count: 3
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 20
+
+insert into test values (null);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 20
+
+select median(distinct v) from test;
+> MEDIAN(DISTINCT V)
+> ------------------
+> 15
+
+insert into test values (10);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 15
+
+drop table test;
+> ok
+
+create table test(v bigint);
+> ok
+
+insert into test values (20), (20), (10);
+> update count: 3
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 20
+
+insert into test values (null);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 20
+
+select median(distinct v) from test;
+> MEDIAN(DISTINCT V)
+> ------------------
+> 15
+
+insert into test values (10);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 15
+
+drop table test;
+> ok
+
+create table test(v real);
+> ok
+
+insert into test values (2), (2), (1);
+> update count: 3
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 2.0
+
+insert into test values (null);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 2.0
+
+select median(distinct v) from test;
+> MEDIAN(DISTINCT V)
+> ------------------
+> 1.5
+
+insert into test values (1);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 1.5
+
+drop table test;
+> ok
+
+create table test(v double);
+> ok
+
+insert into test values (2), (2), (1);
+> update count: 3
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 2.0
+
+insert into test values (null);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 2.0
+
+select median(distinct v) from test;
+> MEDIAN(DISTINCT V)
+> ------------------
+> 1.5
+
+insert into test values (1);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 1.5
+
+drop table test;
+> ok
+
+create table test(v numeric(1));
+> ok
+
+insert into test values (2), (2), (1);
+> update count: 3
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 2
+
+insert into test values (null);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 2
+
+select median(distinct v) from test;
+> MEDIAN(DISTINCT V)
+> ------------------
+> 1.5
+
+insert into test values (1);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 1.5
+
+drop table test;
+> ok
+
+create table test(v time);
+> ok
+
+insert into test values ('20:00:00'), ('20:00:00'), ('10:00:00');
+> update count: 3
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 20:00:00
+
+insert into test values (null);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 20:00:00
+
+select median(distinct v) from test;
+> MEDIAN(DISTINCT V)
+> ------------------
+> 15:00:00
+
+insert into test values ('10:00:00');
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------
+> 15:00:00
+
+drop table test;
+> ok
+
+create table test(v date);
+> ok
+
+insert into test values ('2000-01-20'), ('2000-01-20'), ('2000-01-10');
+> update count: 3
+
+select median(v) from test;
+> MEDIAN(V)
+> ----------
+> 2000-01-20
+
+insert into test values (null);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ----------
+> 2000-01-20
+
+select median(distinct v) from test;
+> MEDIAN(DISTINCT V)
+> ------------------
+> 2000-01-15
+
+insert into test values ('2000-01-10');
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ----------
+> 2000-01-15
+
+drop table test;
+> ok
+
+create table test(v timestamp);
+> ok
+
+insert into test values ('2000-01-20 20:00:00'), ('2000-01-20 20:00:00'), ('2000-01-10 10:00:00');
+> update count: 3
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------------------
+> 2000-01-20 20:00:00.0
+
+insert into test values (null);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------------------
+> 2000-01-20 20:00:00.0
+
+select median(distinct v) from test;
+> MEDIAN(DISTINCT V)
+> ---------------------
+> 2000-01-15 15:00:00.0
+
+insert into test values ('2000-01-10 10:00:00');
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------------------
+> 2000-01-15 15:00:00.0
+
+delete from test;
+> update count: 5
+
+insert into test values ('2000-01-20 20:00:00'), ('2000-01-21 20:00:00');
+> update count: 2
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------------------
+> 2000-01-21 08:00:00.0
+
+drop table test;
+> ok
+
+create table test(v timestamp with time zone);
+> ok
+
+insert into test values ('2000-01-20 20:00:00+04'), ('2000-01-20 20:00:00+04'), ('2000-01-10 10:00:00+02');
+> update count: 3
+
+select median(v) from test;
+> MEDIAN(V)
+> ------------------------
+> 2000-01-20 20:00:00.0+04
+
+insert into test values (null);
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ------------------------
+> 2000-01-20 20:00:00.0+04
+
+select median(distinct v) from test;
+> MEDIAN(DISTINCT V)
+> ------------------------
+> 2000-01-15 15:00:00.0+03
+
+insert into test values ('2000-01-10 10:00:00+02');
+> update count: 1
+
+select median(v) from test;
+> MEDIAN(V)
+> ------------------------
+> 2000-01-15 15:00:00.0+03
+
+delete from test;
+> update count: 5
+
+insert into test values ('2000-01-20 20:00:00+10'), ('2000-01-21 20:00:00-09');
+> update count: 2
+
+select median(v) from test;
+> MEDIAN(V)
+> ---------------------------
+> 2000-01-21 08:00:00.0+00:30
+
+drop table test;
+> ok
+
+-- with group by
+create table test(name varchar, value int);
+> ok
+
+insert into test values ('Group 2A', 10), ('Group 2A', 10), ('Group 2A', 20),
+    ('Group 1X', 40), ('Group 1X', 50), ('Group 3B', null);
+> update count: 6
+
+select name, median(value) from test group by name order by name;
+> NAME     MEDIAN(VALUE)
+> -------- -------------
+> Group 1X 45
+> Group 2A 10
+> Group 3B null
+> rows (ordered): 3
+
+drop table test;
+> ok