Add LEAD() and LAG() window functions

h2/src/docsrc/help/help.csv

@@ -5176,6 +5176,46 @@ SELECT CUME_DIST() OVER (ORDER BY ID), * FROM TEST;
 SELECT CUME_DIST() OVER (PARTITION BY CATEGORY ORDER BY ID), * FROM TEST;
 "
 
+"Functions (Window)","LEAD","
+LEAD(value [, offsetInt [, defaultValue]]) [{RESPECT|IGNORE} NULLS]
+OVER windowSpecification
+","
+Returns the value in a next row with specified offset relative to the current row.
+Offset must be non-negative.
+If IGNORE NULLS is specified rows with null values in selected expression are skipped.
+If number of considered rows is less than specified relative number this function returns NULL
+or the specified default value, if any.
+If offset is 0 the value from the current row is returned unconditionally.
+
+Window functions are currently experimental in H2 and should be used with caution.
+They also may require a lot of memory for large queries.
+","
+SELECT LEAD(X) OVER (ORDER BY ID), * FROM TEST;
+SELECT LEAD(X, 2, 0) IGNORE NULLS OVER (
+    PARTITION BY CATEGORY ORDER BY ID
+), * FROM TEST;
+"
+
+"Functions (Window)","LAG","
+LAG(value [, offsetInt [, defaultValue]]) [{RESPECT|IGNORE} NULLS]
+OVER windowSpecification
+","
+Returns the value in a previous row with specified offset relative to the current row.
+Offset must be non-negative.
+If IGNORE NULLS is specified rows with null values in selected expression are skipped.
+If number of considered rows is less than specified relative number this function returns NULL
+or the specified default value, if any.
+If offset is 0 the value from the current row is returned unconditionally.
+
+Window functions are currently experimental in H2 and should be used with caution.
+They also may require a lot of memory for large queries.
+","
+SELECT LAG(X) OVER (ORDER BY ID), * FROM TEST;
+SELECT LAG(X, 2, 0) IGNORE NULLS OVER (
+    PARTITION BY CATEGORY ORDER BY ID
+), * FROM TEST;
+"
+
 "Functions (Window)","FIRST_VALUE","
 FIRST_VALUE(value) [{RESPECT|IGNORE} NULLS] OVER windowSpecification
 ","

h2/src/main/org/h2/command/Parser.java

@@ -181,7 +181,7 @@ import org.h2.expression.aggregate.WindowFrameBoundType;
 import org.h2.expression.aggregate.WindowFrameExclusion;
 import org.h2.expression.aggregate.WindowFrameUnits;
 import org.h2.expression.aggregate.WindowFunction;
-import org.h2.expression.aggregate.WindowFunction.WindowFunctionType;
+import org.h2.expression.aggregate.WindowFunctionType;
 import org.h2.index.Index;
 import org.h2.message.DbException;
 import org.h2.result.SortOrder;
@@ -3376,15 +3376,34 @@ public class Parser {
         if (currentSelect == null) {
             throw getSyntaxError();
         }
-        int numArgs = WindowFunction.getArgumentCount(type);
+        int numArgs = WindowFunction.getMinArgumentCount(type);
         Expression[] args = null;
         if (numArgs > 0) {
-            args = new Expression[numArgs];
-            for (int i = 0; i < numArgs; i++) {
-                if (i > 0) {
-                    read(COMMA);
+            // There is no functions with numArgs == 0 && numArgsMax > 0
+            int numArgsMax = WindowFunction.getMaxArgumentCount(type);
+            args = new Expression[numArgsMax];
+            if (numArgs == numArgsMax) {
+                for (int i = 0; i < numArgs; i++) {
+                    if (i > 0) {
+                        read(COMMA);
+                    }
+                    args[i] = readExpression();
+                }
+            } else {
+                int i = 0;
+                while (i < numArgsMax) {
+                    if (i > 0 && !readIf(COMMA)) {
+                        break;
+                    }
+                    args[i] = readExpression();
+                    i++;
+                }
+                if (i < numArgs) {
+                    throw getSyntaxError();
+                }
+                if (i != numArgsMax) {
+                    args = Arrays.copyOf(args, i);
                 }
-                args[i] = readExpression();
             }
         }
         read(CLOSE_PAREN);
@@ -3393,6 +3412,8 @@ public class Parser {
             readFromFirstOrLast(function);
         }
         switch (type) {
+        case LEAD:
+        case LAG:
         case FIRST_VALUE:
         case LAST_VALUE:
         case NTH_VALUE:

h2/src/main/org/h2/expression/aggregate/WindowFunctionType.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.aggregate;
+
+/**
+ * A type of a window function.
+ */
+public enum WindowFunctionType {
+
+    /**
+     * The type for ROW_NUMBER() window function.
+     */
+    ROW_NUMBER,
+
+    /**
+     * The type for RANK() window function.
+     */
+    RANK,
+
+    /**
+     * The type for DENSE_RANK() window function.
+     */
+    DENSE_RANK,
+
+    /**
+     * The type for PERCENT_RANK() window function.
+     */
+    PERCENT_RANK,
+
+    /**
+     * The type for CUME_DIST() window function.
+     */
+    CUME_DIST,
+
+    /**
+     * The type for LEAD() window function.
+     */
+    LEAD,
+
+    /**
+     * The type for LAG() window function.
+     */
+    LAG,
+
+    /**
+     * The type for FIRST_VALUE() window function.
+     */
+    FIRST_VALUE,
+
+    /**
+     * The type for LAST_VALUE() window function.
+     */
+    LAST_VALUE,
+
+    /**
+     * The type for NTH_VALUE() window function.
+     */
+    NTH_VALUE,
+
+    ;
+
+    /**
+     * Returns the type of window function with the specified name, or null.
+     *
+     * @param name
+     *            name of a window function
+     * @return the type of window function, or null.
+     */
+    public static WindowFunctionType get(String name) {
+        switch (name) {
+        case "ROW_NUMBER":
+            return ROW_NUMBER;
+        case "RANK":
+            return RANK;
+        case "DENSE_RANK":
+            return DENSE_RANK;
+        case "PERCENT_RANK":
+            return PERCENT_RANK;
+        case "CUME_DIST":
+            return CUME_DIST;
+        case "LEAD":
+            return LEAD;
+        case "LAG":
+            return LAG;
+        case "FIRST_VALUE":
+            return FIRST_VALUE;
+        case "LAST_VALUE":
+            return LAST_VALUE;
+        case "NTH_VALUE":
+            return NTH_VALUE;
+        default:
+            return null;
+        }
+    }
+
+}
\ No newline at end of file

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

@@ -179,7 +179,7 @@ public class TestScript extends TestDb {
                 "parsedatetime", "quarter", "second", "truncate", "week", "year", "date_trunc" }) {
             testScript("functions/timeanddate/" + s + ".sql");
         }
-        for (String s : new String[] { "row_number", "nth_value" }) {
+        for (String s : new String[] { "lead", "row_number", "nth_value" }) {
             testScript("functions/window/" + s + ".sql");
         }
 

h2/src/test/org/h2/test/scripts/functions/aggregate/array-agg.sql

@@ -394,14 +394,14 @@ CREATE TABLE TEST (ID INT, VALUE INT);
 > ok
 
 INSERT INTO TEST VALUES
-  (1, 1),
-  (2, 1),
-  (3, 2),
-  (4, 2),
-  (5, 3),
-  (6, 3),
-  (7, 4),
-  (8, 4);
+    (1, 1),
+    (2, 1),
+    (3, 2),
+    (4, 2),
+    (5, 3),
+    (6, 3),
+    (7, 4),
+    (8, 4);
 > update count: 8
 
 SELECT *, ARRAY_AGG(ID) OVER (ORDER BY VALUE RANGE BETWEEN 2 PRECEDING AND 1 PRECEDING) FROM TEST;

h2/src/test/org/h2/test/scripts/functions/window/lead.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
+--
+
+CREATE TABLE TEST (ID INT PRIMARY KEY, VALUE INT);
+> ok
+
+INSERT INTO TEST VALUES
+    (1, NULL),
+    (2, 12),
+    (3, NULL),
+    (4, 13),
+    (5, NULL),
+    (6, 21),
+    (7, 22),
+    (8, 33),
+    (9, NULL);
+> update count: 9
+
+SELECT *,
+    LEAD(VALUE) OVER (ORDER BY ID) LD,
+    LEAD(VALUE) RESPECT NULLS OVER (ORDER BY ID) LD_N,
+    LEAD(VALUE) IGNORE NULLS OVER (ORDER BY ID) LD_NN,
+    LAG(VALUE) OVER (ORDER BY ID) LG,
+    LAG(VALUE) RESPECT NULLS OVER (ORDER BY ID) LG_N,
+    LAG(VALUE) IGNORE NULLS OVER (ORDER BY ID) LG_NN
+    FROM TEST;
+> ID VALUE LD   LD_N LD_NN LG   LG_N LG_NN
+> -- ----- ---- ---- ----- ---- ---- -----
+> 1  null  12   12   12    null null null
+> 2  12    null null 13    null null null
+> 3  null  13   13   13    12   12   12
+> 4  13    null null 21    null null 12
+> 5  null  21   21   21    13   13   13
+> 6  21    22   22   22    null null 13
+> 7  22    33   33   33    21   21   21
+> 8  33    null null null  22   22   22
+> 9  null  null null null  33   33   33
+> rows (ordered): 9
+
+SELECT *,
+    LEAD(VALUE, 1) OVER (ORDER BY ID) LD,
+    LEAD(VALUE, 1) RESPECT NULLS OVER (ORDER BY ID) LD_N,
+    LEAD(VALUE, 1) IGNORE NULLS OVER (ORDER BY ID) LD_NN,
+    LAG(VALUE, 1) OVER (ORDER BY ID) LG,
+    LAG(VALUE, 1) RESPECT NULLS OVER (ORDER BY ID) LG_N,
+    LAG(VALUE, 1) IGNORE NULLS OVER (ORDER BY ID) LG_NN
+    FROM TEST;
+> ID VALUE LD   LD_N LD_NN LG   LG_N LG_NN
+> -- ----- ---- ---- ----- ---- ---- -----
+> 1  null  12   12   12    null null null
+> 2  12    null null 13    null null null
+> 3  null  13   13   13    12   12   12
+> 4  13    null null 21    null null 12
+> 5  null  21   21   21    13   13   13
+> 6  21    22   22   22    null null 13
+> 7  22    33   33   33    21   21   21
+> 8  33    null null null  22   22   22
+> 9  null  null null null  33   33   33
+> rows (ordered): 9
+
+SELECT *,
+    LEAD(VALUE, 0) OVER (ORDER BY ID) LD,
+    LEAD(VALUE, 0) RESPECT NULLS OVER (ORDER BY ID) LD_N,
+    LEAD(VALUE, 0) IGNORE NULLS OVER (ORDER BY ID) LD_NN,
+    LAG(VALUE, 0) OVER (ORDER BY ID) LG,
+    LAG(VALUE, 0) RESPECT NULLS OVER (ORDER BY ID) LG_N,
+    LAG(VALUE, 0) IGNORE NULLS OVER (ORDER BY ID) LG_NN
+    FROM TEST;
+> ID VALUE LD   LD_N LD_NN LG   LG_N LG_NN
+> -- ----- ---- ---- ----- ---- ---- -----
+> 1  null  null null null  null null null
+> 2  12    12   12   12    12   12   12
+> 3  null  null null null  null null null
+> 4  13    13   13   13    13   13   13
+> 5  null  null null null  null null null
+> 6  21    21   21   21    21   21   21
+> 7  22    22   22   22    22   22   22
+> 8  33    33   33   33    33   33   33
+> 9  null  null null null  null null null
+> rows (ordered): 9
+
+SELECT *,
+    LEAD(VALUE, 2) OVER (ORDER BY ID) LD,
+    LEAD(VALUE, 2) RESPECT NULLS OVER (ORDER BY ID) LD_N,
+    LEAD(VALUE, 2) IGNORE NULLS OVER (ORDER BY ID) LD_NN,
+    LAG(VALUE, 2) OVER (ORDER BY ID) LG,
+    LAG(VALUE, 2) RESPECT NULLS OVER (ORDER BY ID) LG_N,
+    LAG(VALUE, 2) IGNORE NULLS OVER (ORDER BY ID) LG_NN
+    FROM TEST;
+> ID VALUE LD   LD_N LD_NN LG   LG_N LG_NN
+> -- ----- ---- ---- ----- ---- ---- -----
+> 1  null  null null 13    null null null
+> 2  12    13   13   21    null null null
+> 3  null  null null 21    null null null
+> 4  13    21   21   22    12   12   null
+> 5  null  22   22   22    null null 12
+> 6  21    33   33   33    13   13   12
+> 7  22    null null null  null null 13
+> 8  33    null null null  21   21   21
+> 9  null  null null null  22   22   22
+> rows (ordered): 9
+
+SELECT *,
+    LEAD(VALUE, 2, 1111.0) OVER (ORDER BY ID) LD,
+    LEAD(VALUE, 2, 1111.0) RESPECT NULLS OVER (ORDER BY ID) LD_N,
+    LEAD(VALUE, 2, 1111.0) IGNORE NULLS OVER (ORDER BY ID) LD_NN,
+    LAG(VALUE, 2, 1111.0) OVER (ORDER BY ID) LG,
+    LAG(VALUE, 2, 1111.0) RESPECT NULLS OVER (ORDER BY ID) LG_N,
+    LAG(VALUE, 2, 1111.0) IGNORE NULLS OVER (ORDER BY ID) LG_NN
+    FROM TEST;
+> ID VALUE LD   LD_N LD_NN LG   LG_N LG_NN
+> -- ----- ---- ---- ----- ---- ---- -----
+> 1  null  null null 13    1111 1111 1111
+> 2  12    13   13   21    1111 1111 1111
+> 3  null  null null 21    null null 1111
+> 4  13    21   21   22    12   12   1111
+> 5  null  22   22   22    null null 12
+> 6  21    33   33   33    13   13   12
+> 7  22    null null 1111  null null 13
+> 8  33    1111 1111 1111  21   21   21
+> 9  null  1111 1111 1111  22   22   22
+> rows (ordered): 9
+
+SELECT LEAD(VALUE, -1) OVER (ORDER BY ID) FROM TEST;
+> exception INVALID_VALUE_2
+
+SELECT LAG(VALUE, -1) OVER (ORDER BY ID) FROM TEST;
+> exception INVALID_VALUE_2
+
+DROP TABLE TEST;
+> ok

h2/src/tools/org/h2/build/doc/dictionary.txt

@@ -796,4 +796,4 @@ interior envelopes multilinestring multipoint packed exterior normalization awkw
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 pointzm pointz pointm dimensionality redefine forum measures
 mpg casted pzm mls constrained subtypes complains
-ranks rno dro rko precede cume reopens preceding unbounded rightly itr
+ranks rno dro rko precede cume reopens preceding unbounded rightly itr lag maximal