parser: support empty target list in SELECT

This commit adds support for parsing empty target list for SELECT stmts (i.e. queries of the form `SELECT;`, `SELECT ALL FROM t;`, `SELECT FROM t;` where the projection column list is omitted). Apparently, some tools like hasura use it to get the row count. This is achieved by making `target_list` optional. However, the caveat is that the new parsing rule runs into a shift/reduce conflict with `SELECT error` rule (since now both options can match empty string after `SELECT` AFAICT). I tried adjusting the precedence of the newly adjusted rule to resolve this conflict but didn't succeed (Raphael tried doing the same with the same result). Release note (sql change): CockroachDB now supports parsing queries like `SELECT FROM t` that only produce the row count and do not output any columns.
renatolabs · Jan 4, 2024 · da147cf · da147cf
1 parent cbe17c3
commit da147cf
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Showing 10 changed files with 46 additions and 27 deletions.
diff --git a/docs/generated/sql/bnf/simple_select_clause.bnf b/docs/generated/sql/bnf/simple_select_clause.bnf
@@ -1,4 +1,4 @@
 simple_select_clause ::=
-	'SELECT' ( 'ALL' |  ) ( ( target_elem ) ( ( ',' target_elem ) )* ) ( 'FROM' ( ( table_ref ) ( ( ',' table_ref ) )* ) ( ( 'AS' 'OF' 'SYSTEM' 'TIME' a_expr ) |  ) |  ) ( ( 'WHERE' a_expr ) |  ) ( 'GROUP' 'BY' group_by_list |  ) ( 'HAVING' a_expr |  ) ( 'WINDOW' window_definition_list |  )
+	'SELECT' ( 'ALL' |  ) opt_target_list ( 'FROM' ( ( table_ref ) ( ( ',' table_ref ) )* ) ( ( 'AS' 'OF' 'SYSTEM' 'TIME' a_expr ) |  ) |  ) ( ( 'WHERE' a_expr ) |  ) ( 'GROUP' 'BY' group_by_list |  ) ( 'HAVING' a_expr |  ) ( 'WINDOW' window_definition_list |  )
 	| 'SELECT' ( 'DISTINCT' ) ( ( target_elem ) ( ( ',' target_elem ) )* ) ( 'FROM' ( ( table_ref ) ( ( ',' table_ref ) )* ) ( ( 'AS' 'OF' 'SYSTEM' 'TIME' a_expr ) |  ) |  ) ( ( 'WHERE' a_expr ) |  ) ( 'GROUP' 'BY' group_by_list |  ) ( 'HAVING' a_expr |  ) ( 'WINDOW' window_definition_list |  )
 	| 'SELECT' ( 'DISTINCT' 'ON' '(' ( ( a_expr ) ( ( ',' a_expr ) )* ) ')' ) ( ( target_elem ) ( ( ',' target_elem ) )* ) ( 'FROM' ( ( table_ref ) ( ( ',' table_ref ) )* ) ( ( 'AS' 'OF' 'SYSTEM' 'TIME' a_expr ) |  ) |  ) ( ( 'WHERE' a_expr ) |  ) ( 'GROUP' 'BY' group_by_list |  ) ( 'HAVING' a_expr |  ) ( 'WINDOW' window_definition_list |  )
diff --git a/docs/generated/sql/bnf/stmt_block.bnf b/docs/generated/sql/bnf/stmt_block.bnf
@@ -2722,7 +2722,7 @@ scrub_option_list ::=
 	( scrub_option ) ( ( ',' scrub_option ) )*
 
 simple_select_clause ::=
-	'SELECT' opt_all_clause target_list from_clause opt_where_clause group_clause having_clause window_clause
+	'SELECT' opt_all_clause opt_target_list from_clause opt_where_clause group_clause having_clause window_clause
 	| 'SELECT' distinct_clause target_list from_clause opt_where_clause group_clause having_clause window_clause
 	| 'SELECT' distinct_on_clause target_list from_clause opt_where_clause group_clause having_clause window_clause
 
@@ -3288,6 +3288,10 @@ opt_all_clause ::=
 	'ALL'
 	| 
 
+opt_target_list ::=
+	target_list
+	| 
+
 from_clause ::=
 	'FROM' from_list opt_as_of_clause
 	| 

diff --git a/pkg/cli/clisqlshell/sql_test.go b/pkg/cli/clisqlshell/sql_test.go
@@ -335,14 +335,12 @@ func Example_includes() {
 	// SELECT -- incomplete statement, \i invalid
 	// \i testdata/i_twolevels2.sql
 	// ^
-	// HINT: try \h SELECT
 	// ERROR: at or near "\": syntax error
 	// SQLSTATE: 42601
 	// DETAIL: source SQL:
 	// SELECT -- incomplete statement, \i invalid
 	// \i testdata/i_twolevels2.sql
 	// ^
-	// HINT: try \h SELECT
 	// sql -f testdata/i_stopmiddle.sql
 	// ?column?
 	// 123

diff --git a/pkg/cli/interactive_tests/test_contextual_help.tcl b/pkg/cli/interactive_tests/test_contextual_help.tcl
@@ -72,7 +72,6 @@ eexpect "use '??'"
 eexpect " ->"
 # restore the normal state
 send ";\r"
-eexpect HINT
 eexpect root@
 end_test
 

diff --git a/pkg/sql/logictest/testdata/logic_test/select b/pkg/sql/logictest/testdata/logic_test/select
@@ -21,7 +21,7 @@ two four
 statement ok
 CREATE TABLE abc (a INT PRIMARY KEY, b INT, c INT)
 
-query error at or near "from": syntax error
+statement ok
 SELECT FROM abc
 
 query error could not parse "hello" as type bool

diff --git a/pkg/sql/parser/help_test.go b/pkg/sql/parser/help_test.go
@@ -495,7 +495,6 @@ func TestContextualHelp(t *testing.T) {
 		{`SELECT * FROM ??`, `<SOURCE>`},
 		{`SELECT 1 AS OF ??`, `SELECT`},
 		{`SELECT 1 FROM foo ??`, `SELECT`},
-		{`SELECT 1 FROM foo WHERE ??`, `SELECT`},
 		{`SELECT 1 FROM (SELECT ??`, `SELECT`},
 		{`SELECT 1 FROM (VALUES ??`, `VALUES`},
 		{`SELECT 1 FROM (TABLE ??`, `TABLE`},

diff --git a/pkg/sql/parser/sql.y b/pkg/sql/parser/sql.y
@@ -1478,7 +1478,7 @@ func (u *sqlSymUnion) showFingerprintOptions() *tree.ShowFingerprintOptions {
 %type <*tree.Tuple> expr_tuple1_ambiguous expr_tuple_unambiguous
 %type <tree.NameList> attrs
 %type <[]string> session_var_parts
-%type <tree.SelectExprs> target_list
+%type <tree.SelectExprs> opt_target_list target_list
 %type <tree.UpdateExprs> set_clause_list
 %type <*tree.UpdateExpr> set_clause multiple_set_clause
 %type <tree.ArraySubscripts> array_subscripts
@@ -12770,7 +12770,7 @@ simple_select:
 //        [ OFFSET <expr> [ ROW | ROWS ] ]
 // %SeeAlso: WEBDOCS/select-clause.html
 simple_select_clause:
-  SELECT opt_all_clause target_list
+  SELECT opt_all_clause opt_target_list
     from_clause opt_where_clause
     group_clause having_clause window_clause
   {
@@ -12812,7 +12812,6 @@ simple_select_clause:
       Window:     $8.window(),
     }
   }
-| SELECT error // SHOW HELP: SELECT
 
 set_operation:
   select_clause UNION all_or_distinct select_clause
@@ -16266,6 +16265,16 @@ target_list:
     $$.val = append($1.selExprs(), $3.selExpr())
   }
 
+opt_target_list:
+  target_list
+  {
+    $$.val = $1.selExprs()
+  }
+| /* EMPTY */
+  {
+    $$.val = tree.SelectExprs{}
+  }
+
 target_elem:
   a_expr AS target_name
   {

diff --git a/pkg/sql/parser/testdata/predefined_functions b/pkg/sql/parser/testdata/predefined_functions
@@ -189,7 +189,6 @@ at or near ",": syntax error
 DETAIL: source SQL:
 SELECT POSITION('high', 'a')
                       ^
-HINT: try \h SELECT
 
 parse
 SELECT OVERLAY('w33333rce' PLACING 'resou' FROM 3)

diff --git a/pkg/sql/parser/testdata/select_clauses b/pkg/sql/parser/testdata/select_clauses
@@ -1488,7 +1488,6 @@ at or near "EOF": syntax error
 DETAIL: source SQL:
 SELECT * FROM t WHERE k=
                         ^
-HINT: try \h SELECT
 
 parse
 SELECT a FROM t ORDER BY a

diff --git a/pkg/sql/parser/testdata/select_exprs b/pkg/sql/parser/testdata/select_exprs
@@ -1,3 +1,11 @@
+parse
+SELECT
+----
+SELECT  -- normalized!
+SELECT  -- fully parenthesized
+SELECT  -- literals removed
+SELECT  -- identifiers removed
+
 parse
 SELECT 1 + 1
 ----
@@ -77,7 +85,6 @@ lexical error: invalid floating point literal
 DETAIL: source SQL:
 SELECT 1e-\n-1
        ^
-HINT: try \h SELECT
 
 parse
 SELECT *,-/* comment */-5
@@ -651,7 +658,6 @@ at or near "5": syntax error
 DETAIL: source SQL:
 SELECT 1 ||/ 5
              ^
-HINT: try \h SELECT
 
 
 parse
@@ -1390,7 +1396,6 @@ lexical error: invalid hexadecimal numeric literal
 DETAIL: source SQL:
 SELECT 0x FROM t
        ^
-HINT: try \h SELECT
 
 error
 SELECT x'fail' FROM t
@@ -1399,7 +1404,6 @@ lexical error: invalid hexadecimal bytes literal
 DETAIL: source SQL:
 SELECT x'fail' FROM t
        ^
-HINT: try \h SELECT
 
 error
 SELECT x'AAB' FROM t
@@ -1408,7 +1412,6 @@ lexical error: invalid hexadecimal bytes literal
 DETAIL: source SQL:
 SELECT x'AAB' FROM t
        ^
-HINT: try \h SELECT
 
 parse
 SELECT CAST(1 AS STRING)
@@ -1848,7 +1851,6 @@ lexical error: unterminated string
 DETAIL: source SQL:
 SELECT '1
        ^
-HINT: try \h SELECT
 
 error
 SELECT family FROM test
@@ -1857,16 +1859,30 @@ at or near "from": syntax error
 DETAIL: source SQL:
 SELECT family FROM test
               ^
-HINT: try \h SELECT
 
-error
+parse
 SELECT FROM t
 ----
+SELECT  FROM t -- normalized!
+SELECT  FROM t -- fully parenthesized
+SELECT  FROM t -- literals removed
+SELECT  FROM _ -- identifiers removed
+
+parse
+SELECT ALL FROM t
+----
+SELECT  FROM t -- normalized!
+SELECT  FROM t -- fully parenthesized
+SELECT  FROM t -- literals removed
+SELECT  FROM _ -- identifiers removed
+
+error
+SELECT DISTINCT FROM test
+----
 at or near "from": syntax error
 DETAIL: source SQL:
-SELECT FROM t
-       ^
-HINT: try \h SELECT
+SELECT DISTINCT FROM test
+                ^
 
 error
 SELECT $0
@@ -1875,7 +1891,6 @@ lexical error: placeholder index must be between 1 and 65536
 DETAIL: source SQL:
 SELECT $0
        ^
-HINT: try \h SELECT
 
 error
 SELECT $-1
@@ -1884,7 +1899,6 @@ at or near "$": syntax error
 DETAIL: source SQL:
 SELECT $-1
        ^
-HINT: try \h SELECT
 
 error
 SELECT $123456789
@@ -1893,7 +1907,6 @@ lexical error: placeholder index must be between 1 and 65536
 DETAIL: source SQL:
 SELECT $123456789
        ^
-HINT: try \h SELECT
 
 error
 SELECT (0) FROM y[array[]]
@@ -2021,7 +2034,6 @@ DATE '2000-03-03')
 OVERLAPS
 (DATE '2000-01-03')
                   ^
-HINT: try \h SELECT
 
 parse
 SELECT NOT ('a' ~ ANY (ARRAY['x']:::STRING[]))