copy: fix copy grammar to match PG

Previously COPY would allow a wide range of syntax in the COPY
TO substatement.  Now like PG we limit it to a few things.

PG grammar is:
```
PreparableStmt:
			SelectStmt
			| InsertStmt
			| UpdateStmt
			| DeleteStmt
			| MergeStmt
```

And now we do something similar. This prevents the wheels from coming
off when RSG generates EXPLAIN's in the substatement for instance.

Release note: none
Epic: none

docs/generated/sql/bnf/BUILD.bazel

@@ -82,6 +82,7 @@ FILES = [
     "comment",
     "commit_transaction",
     "copy_stmt",
+    "copy_to_stmt",
     "create_as_col_qual_list",
     "create_as_constraint_def",
     "create_changefeed_stmt",

docs/generated/sql/bnf/copy_stmt.bnf

@@ -9,8 +9,8 @@ copy_stmt ::=
 	| 'COPY' table_name opt_column_list 'TO' 'STDOUT' 'WITH' '(' copy_generic_options_list ')'
 	| 'COPY' table_name opt_column_list 'TO' 'STDOUT'  '(' copy_generic_options_list ')'
 	| 'COPY' table_name opt_column_list 'TO' 'STDOUT' 
-	| 'COPY' '(' preparable_stmt ')' 'TO' 'STDOUT' 'WITH' copy_options ( ( copy_options ) )*
-	| 'COPY' '(' preparable_stmt ')' 'TO' 'STDOUT'  copy_options ( ( copy_options ) )*
-	| 'COPY' '(' preparable_stmt ')' 'TO' 'STDOUT' 'WITH' '(' copy_generic_options_list ')'
-	| 'COPY' '(' preparable_stmt ')' 'TO' 'STDOUT'  '(' copy_generic_options_list ')'
-	| 'COPY' '(' preparable_stmt ')' 'TO' 'STDOUT' 
+	| 'COPY' '(' copy_to_stmt ')' 'TO' 'STDOUT' 'WITH' copy_options ( ( copy_options ) )*
+	| 'COPY' '(' copy_to_stmt ')' 'TO' 'STDOUT'  copy_options ( ( copy_options ) )*
+	| 'COPY' '(' copy_to_stmt ')' 'TO' 'STDOUT' 'WITH' '(' copy_generic_options_list ')'
+	| 'COPY' '(' copy_to_stmt ')' 'TO' 'STDOUT'  '(' copy_generic_options_list ')'
+	| 'COPY' '(' copy_to_stmt ')' 'TO' 'STDOUT' 

docs/generated/sql/bnf/copy_to_stmt.bnf

@@ -0,0 +1,6 @@
+copy_to_stmt ::=
+	delete_stmt
+	| insert_stmt
+	| select_stmt
+	| update_stmt
+	| upsert_stmt

docs/generated/sql/bnf/stmt_block.bnf

@@ -66,7 +66,7 @@ analyze_stmt ::=
 copy_stmt ::=
 	'COPY' table_name opt_column_list 'FROM' 'STDIN' opt_with_copy_options opt_where_clause
 	| 'COPY' table_name opt_column_list 'TO' 'STDOUT' opt_with_copy_options
-	| 'COPY' '(' preparable_stmt ')' 'TO' 'STDOUT' opt_with_copy_options
+	| 'COPY' '(' copy_to_stmt ')' 'TO' 'STDOUT' opt_with_copy_options
 
 comment_stmt ::=
 	'COMMENT' 'ON' 'DATABASE' database_name 'IS' comment_text
@@ -332,6 +332,13 @@ opt_where_clause ::=
 	where_clause
 	| 
 
+copy_to_stmt ::=
+	delete_stmt
+	| insert_stmt
+	| select_stmt
+	| update_stmt
+	| upsert_stmt
+
 database_name ::=
 	name
 

pkg/gen/bnf.bzl

@@ -82,6 +82,7 @@ BNF_SRCS = [
     "//docs/generated/sql/bnf:comment.bnf",
     "//docs/generated/sql/bnf:commit_transaction.bnf",
     "//docs/generated/sql/bnf:copy_stmt.bnf",
+    "//docs/generated/sql/bnf:copy_to_stmt.bnf",
     "//docs/generated/sql/bnf:create_as_col_qual_list.bnf",
     "//docs/generated/sql/bnf:create_as_constraint_def.bnf",
     "//docs/generated/sql/bnf:create_changefeed_stmt.bnf",

pkg/gen/diagrams.bzl

@@ -82,6 +82,7 @@ DIAGRAMS_SRCS = [
     "//docs/generated/sql/bnf:comment.html",
     "//docs/generated/sql/bnf:commit_transaction.html",
     "//docs/generated/sql/bnf:copy.html",
+    "//docs/generated/sql/bnf:copy_to.html",
     "//docs/generated/sql/bnf:create.html",
     "//docs/generated/sql/bnf:create_as_col_qual_list.html",
     "//docs/generated/sql/bnf:create_as_constraint_def.html",

pkg/gen/docs.bzl

@@ -94,6 +94,7 @@ DOCS_SRCS = [
     "//docs/generated/sql/bnf:comment.bnf",
     "//docs/generated/sql/bnf:commit_transaction.bnf",
     "//docs/generated/sql/bnf:copy_stmt.bnf",
+    "//docs/generated/sql/bnf:copy_to_stmt.bnf",
     "//docs/generated/sql/bnf:create_as_col_qual_list.bnf",
     "//docs/generated/sql/bnf:create_as_constraint_def.bnf",
     "//docs/generated/sql/bnf:create_changefeed_stmt.bnf",

pkg/sql/parser/sql.y

@@ -1207,6 +1207,7 @@ func (u *sqlSymUnion) showCreateFormatOption() tree.ShowCreateFormatOption {
 %type <tree.Statement> preparable_stmt
 %type <tree.Statement> explainable_stmt
 %type <tree.Statement> row_source_extension_stmt
+%type <tree.Statement> copy_to_stmt
 %type <tree.Statement> export_stmt
 %type <tree.Statement> execute_stmt
 %type <tree.Statement> deallocate_stmt
@@ -3977,15 +3978,15 @@ copy_stmt:
   {
     return unimplementedWithIssue(sqllex, 97181)
   }
-| COPY '(' preparable_stmt ')' TO STDOUT opt_with_copy_options
+| COPY '(' copy_to_stmt ')' TO STDOUT opt_with_copy_options
    {
      /* FORCE DOC */
      $$.val = &tree.CopyTo{
         Statement: $3.stmt(),
         Options: *$7.copyOptions(),
      }
    }
-| COPY '(' preparable_stmt ')' TO error
+| COPY '(' copy_to_stmt ')' TO error
    {
      return unimplementedWithIssue(sqllex, 96590)
    }
@@ -5680,6 +5681,16 @@ row_source_extension_stmt:
 | update_stmt       // EXTEND WITH HELP: UPDATE
 | upsert_stmt       // EXTEND WITH HELP: UPSERT
 
+copy_to_stmt:
+  delete_stmt       // EXTEND WITH HELP: DELETE
+| insert_stmt       // EXTEND WITH HELP: INSERT
+| select_stmt       // help texts in sub-rule
+  {
+    $$.val = $1.slct()
+  }
+| update_stmt       // EXTEND WITH HELP: UPDATE
+| upsert_stmt       // EXTEND WITH HELP: UPSERT
+
 explain_option_list:
   explain_option_name
   {

pkg/sql/parser/testdata/copy

@@ -380,3 +380,11 @@ COPY (SELECT * FROM t) TO STDOUT (HEADER, OIDS)
                                               ^
 HINT: You have attempted to use a feature that is not yet implemented.
 See: https://go.crdb.dev/issue-v/41608/
+
+error
+COPY (EXPLAIN SELECT * FROM t) TO STDOUT
+----
+at or near "explain": syntax error
+DETAIL: source SQL:
+COPY (EXPLAIN SELECT * FROM t) TO STDOUT
+      ^