Allow SQL standard FETCH without OFFSET

src/Parsers/ParserSelectQuery.cpp

@@ -292,6 +292,9 @@ bool ParserSelectQuery::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)
     /// This is needed for TOP expression, because it can also use WITH TIES.
     bool limit_with_ties_occured = false;
 
+    bool has_offset_clause = false;
+    bool offset_clause_has_sql_standard_row_or_rows = false; /// OFFSET offset_row_count {ROW | ROWS}
+
     /// LIMIT length | LIMIT offset, length | LIMIT count BY expr-list | LIMIT offset, length BY expr-list
     if (s_limit.ignore(pos, expected))
     {
@@ -316,6 +319,8 @@ bool ParserSelectQuery::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)
         {
             if (!exp_elem.parse(pos, limit_offset, expected))
                 return false;
+
+            has_offset_clause = true;
         }
         else if (s_with_ties.ignore(pos, expected))
         {
@@ -351,26 +356,32 @@ bool ParserSelectQuery::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)
     }
     else if (s_offset.ignore(pos, expected))
     {
-        /// OFFSET offset_row_count {ROW | ROWS} FETCH {FIRST | NEXT} fetch_row_count {ROW | ROWS} {ONLY | WITH TIES}
+        /// OFFSET without LIMIT
-        bool offset_with_fetch_maybe = false;
+
+        has_offset_clause = true;
 
         if (!exp_elem.parse(pos, limit_offset, expected))
             return false;
 
+        /// SQL standard OFFSET N ROW[S] ...
+
         if (s_row.ignore(pos, expected))
-        {
+            offset_clause_has_sql_standard_row_or_rows = true;
+
         if (s_rows.ignore(pos, expected))
-                throw Exception(ErrorCodes::ROW_AND_ROWS_TOGETHER, "Can not use ROW and ROWS together");
-            offset_with_fetch_maybe = true;
-        }
-        else if (s_rows.ignore(pos, expected))
         {
-            offset_with_fetch_maybe = true;
+            if (offset_clause_has_sql_standard_row_or_rows)
+                throw Exception(ErrorCodes::ROW_AND_ROWS_TOGETHER, "Can not use ROW and ROWS together");
+
+            offset_clause_has_sql_standard_row_or_rows = true;
+        }
     }
 
-        if (offset_with_fetch_maybe && s_fetch.ignore(pos, expected))
+    /// SQL standard FETCH (either following SQL standard OFFSET or following ORDER BY)
+    if ((!has_offset_clause || offset_clause_has_sql_standard_row_or_rows)
+        && s_fetch.ignore(pos, expected))
     {
-            /// OFFSET FETCH clause must exists with "ORDER BY"
+        /// FETCH clause must exist with "ORDER BY"
         if (!order_expression_list)
             throw Exception(ErrorCodes::OFFSET_FETCH_WITHOUT_ORDER_BY, "Can not use OFFSET FETCH clause without ORDER BY");
 
@@ -406,7 +417,6 @@ bool ParserSelectQuery::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)
             return false;
         }
     }
-    }
 
     if (distinct_on_expression_list)
     {

tests/queries/0_stateless/02790_sql_standard_fetch.reference

@@ -0,0 +1,36 @@
+┌─id─┬─name──┬─department─┬─salary─┐
+│ 25 │ Frank │ it         │    120 │
+│ 23 │ Henry │ it         │    104 │
+│ 24 │ Irene │ it         │    104 │
+│ 33 │ Alice │ sales      │    100 │
+│ 32 │ Dave  │ sales      │     96 │
+└────┴───────┴────────────┴────────┘
+┌─id─┬─name──┬─department─┬─salary─┐
+│ 25 │ Frank │ it         │    120 │
+│ 23 │ Henry │ it         │    104 │
+│ 24 │ Irene │ it         │    104 │
+│ 33 │ Alice │ sales      │    100 │
+│ 32 │ Dave  │ sales      │     96 │
+└────┴───────┴────────────┴────────┘
+┌─id─┬─name──┬─department─┬─salary─┐
+│ 25 │ Frank │ it         │    120 │
+│ 23 │ Henry │ it         │    104 │
+│ 24 │ Irene │ it         │    104 │
+│ 33 │ Alice │ sales      │    100 │
+│ 31 │ Cindy │ sales      │     96 │
+│ 32 │ Dave  │ sales      │     96 │
+└────┴───────┴────────────┴────────┘
+┌─id─┬─name──┬─department─┬─salary─┐
+│ 33 │ Alice │ sales      │    100 │
+│ 31 │ Cindy │ sales      │     96 │
+│ 32 │ Dave  │ sales      │     96 │
+│ 22 │ Grace │ it         │     90 │
+│ 21 │ Emma  │ it         │     84 │
+└────┴───────┴────────────┴────────┘
+┌─id─┬─name──┬─department─┬─salary─┐
+│ 33 │ Alice │ sales      │    100 │
+│ 31 │ Cindy │ sales      │     96 │
+│ 32 │ Dave  │ sales      │     96 │
+│ 22 │ Grace │ it         │     90 │
+│ 21 │ Emma  │ it         │     84 │
+└────┴───────┴────────────┴────────┘

tests/queries/0_stateless/02790_sql_standard_fetch.sql

@@ -0,0 +1,31 @@
+# https://antonz.org/sql-fetch/
+
+CREATE TEMPORARY TABLE employees (id UInt64, name String, department String, salary UInt64);
+INSERT INTO employees VALUES (23, 'Henry', 'it', 104), (24, 'Irene', 'it', 104), (25, 'Frank', 'it', 120), (31, 'Cindy', 'sales', 96), (33, 'Alice', 'sales', 100), (32, 'Dave', 'sales', 96), (22, 'Grace', 'it', 90), (21, 'Emma', 'it', '84');
+
+select * from employees
+order by salary desc
+limit 5
+format PrettyCompactNoEscapes;
+
+select * from employees
+order by salary desc
+fetch first 5 rows only
+format PrettyCompactNoEscapes;
+
+select * from employees
+order by salary desc
+fetch first 5 rows with ties
+format PrettyCompactNoEscapes;
+
+select * from employees
+order by salary desc
+offset 3 rows
+fetch next 5 rows only
+format PrettyCompactNoEscapes;
+
+select * from employees
+order by salary desc
+offset 3 rows
+fetch first 5 rows only
+format PrettyCompactNoEscapes;