Forbid mixed OFFSET/FETCH/LIMIT/TOP clauses and improve documentation

h2/src/docsrc/help/help.csv

@@ -22,9 +22,16 @@ HAVING filter rows after grouping.
 ORDER BY sorts the result by the given column(s) or expression(s).
 UNION combines the result of this query with the results of another query.
 
+Number of rows in output can be limited either with standard OFFSET / FETCH,
+with non-standard LIMIT / OFFSET, or with non-standard TOP clauses.
+Different clauses cannot be used together.
 FETCH FIRST/NEXT, LIMIT or TOP limits the number of rows returned by the query (no limit if null or smaller than zero).
-OFFSET specified how many rows to skip.
-Please note using high offset values should be avoided because it can cause performance problems.
+If PERCENT is specified number of rows is specified as a percent of the total number of rows
+and should be an integer value between 0 and 100 inclusive.
+WITH TIES can be used only together with ORDER BY and means that all additional rows that have the same sorting position
+as the last row will be also returned.
+OFFSET specifies how many rows to skip.
+Please note that queries with high offset values can be slow.
 SAMPLE_SIZE limits the number of rows read for aggregate queries.
 
 Multiple set operators (UNION, INTERSECT, MINUS, EXCEPT) are evaluated
@@ -41,7 +48,8 @@ SELECT * FROM TEST ORDER BY NAME;
 SELECT ID, COUNT(*) FROM TEST GROUP BY ID;
 SELECT NAME, COUNT(*) FROM TEST GROUP BY NAME HAVING COUNT(*) > 2;
 SELECT 'ID' COL, MAX(ID) AS MAX FROM TEST UNION SELECT 'NAME', MAX(NAME) FROM TEST;
-SELECT * FROM TEST LIMIT 1000;
+SELECT * FROM TEST OFFSET 1000 ROWS FETCH NEXT 1000 ROWS ONLY;
+SELECT A, B FROM TEST ORDER BY A FETCH NEXT 10 ROWS WITH TIES;
 SELECT * FROM (SELECT ID, COUNT(*) FROM TEST
     GROUP BY ID UNION SELECT NULL, COUNT(*) FROM TEST)
     ORDER BY 1 NULLS LAST;

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

@@ -2358,59 +2358,64 @@ public class Parser {
             command.setOrder(orderList);
             currentSelect = oldSelect;
         }
-        // make sure aggregate functions will not work here
-        Select temp = currentSelect;
-        currentSelect = null;
-        // Standard SQL OFFSET / FETCH
-        if (readIf(OFFSET)) {
-            command.setOffset(readExpression().optimize(session));
-            if (!readIf("ROW")) {
-                readIf("ROWS");
+        if (command.getLimit() == null) {
+            // make sure aggregate functions will not work here
+            Select temp = currentSelect;
+            currentSelect = null;
+            boolean hasOffsetOrFetch = false;
+            // Standard SQL OFFSET / FETCH
+            if (readIf(OFFSET)) {
+                hasOffsetOrFetch = true;
+                command.setOffset(readExpression().optimize(session));
+                if (!readIf("ROW")) {
+                    readIf("ROWS");
+                }
             }
-        }
-        if (readIf(FETCH)) {
-            if (!readIf("FIRST")) {
-                read("NEXT");
+            if (readIf(FETCH)) {
+                hasOffsetOrFetch = true;
+                if (!readIf("FIRST")) {
+                    read("NEXT");
+                }
+                if (readIf("ROW") || readIf("ROWS")) {
+                    command.setLimit(ValueExpression.get(ValueInt.get(1)));
+                } else {
+                    Expression limit = readExpression().optimize(session);
+                    command.setLimit(limit);
+                    if (readIf("PERCENT")) {
+                        command.setFetchPercent(true);
+                    }
+                    if (!readIf("ROW")) {
+                        read("ROWS");
+                    }
+                }
+                if (readIf(WITH)) {
+                    read("TIES");
+                    command.setWithTies(true);
+                } else {
+                    read("ONLY");
+                }
             }
-            if (readIf("ROW") || readIf("ROWS")) {
-                command.setLimit(ValueExpression.get(ValueInt.get(1)));
-            } else {
+            // MySQL-style LIMIT / OFFSET
+            if (!hasOffsetOrFetch && readIf(LIMIT)) {
                 Expression limit = readExpression().optimize(session);
                 command.setLimit(limit);
-                if (readIf("PERCENT")) {
-                    command.setFetchPercent(true);
-                }
-                if (!readIf("ROW")) {
-                    read("ROWS");
+                if (readIf(OFFSET)) {
+                    Expression offset = readExpression().optimize(session);
+                    command.setOffset(offset);
+                } else if (readIf(COMMA)) {
+                    // MySQL: [offset, ] rowcount
+                    Expression offset = limit;
+                    limit = readExpression().optimize(session);
+                    command.setOffset(offset);
+                    command.setLimit(limit);
                 }
             }
-            if (readIf(WITH)) {
-                read("TIES");
-                command.setWithTies(true);
-            } else {
-                read("ONLY");
+            if (readIf("SAMPLE_SIZE")) {
+                Expression sampleSize = readExpression().optimize(session);
+                command.setSampleSize(sampleSize);
             }
+            currentSelect = temp;
         }
-        // MySQL-style LIMIT / OFFSET
-        if (readIf(LIMIT)) {
-            Expression limit = readExpression().optimize(session);
-            command.setLimit(limit);
-            if (readIf(OFFSET)) {
-                Expression offset = readExpression().optimize(session);
-                command.setOffset(offset);
-            } else if (readIf(COMMA)) {
-                // MySQL: [offset, ] rowcount
-                Expression offset = limit;
-                limit = readExpression().optimize(session);
-                command.setOffset(offset);
-                command.setLimit(limit);
-            }
-        }
-        if (readIf("SAMPLE_SIZE")) {
-            Expression sampleSize = readExpression().optimize(session);
-            command.setSampleSize(sampleSize);
-        }
-        currentSelect = temp;
         if (readIf(FOR)) {
             if (readIf("UPDATE")) {
                 if (readIf("OF")) {

h2/src/test/org/h2/test/scripts/dml/select.sql

@@ -267,3 +267,25 @@ DROP TABLE TEST1;
 
 DROP TABLE TEST2;
 > ok
+
+-- Disallowed mixed OFFSET/FETCH/LIMIT/TOP clauses
+CREATE TABLE TEST (ID BIGINT);
+> ok
+
+SELECT TOP 1 ID FROM TEST OFFSET 1 ROW;
+> exception SYNTAX_ERROR_1
+
+SELECT TOP 1 ID FROM TEST FETCH NEXT ROW ONLY;
+> exception SYNTAX_ERROR_1
+
+SELECT TOP 1 ID FROM TEST LIMIT 1;
+> exception SYNTAX_ERROR_1
+
+SELECT ID FROM TEST OFFSET 1 ROW LIMIT 1;
+> exception SYNTAX_ERROR_1
+
+SELECT ID FROM TEST FETCH NEXT ROW ONLY LIMIT 1;
+> exception SYNTAX_ERROR_1
+
+DROP TABLE TEST;
+> ok