gianm commented on code in PR #5349:
URL: https://github.com/apache/calcite/pull/5349#discussion_r4408437366
##########
core/src/main/codegen/templates/Parser.jj:
##########
@@ -915,6 +923,138 @@ SqlNode LeafQuery(ExprContext exprContext) :
e = TableConstructor() { return e; }
|
e = ExplicitTable(getPos()) { return e; }
+|
+ e = FromQuery() { return e; }
+}
+
+/**
+ * Parses a standalone FROM clause. Only valid under conformance levels
+ * that allow pipe syntax.
+ */
+SqlNode FromQuery() :
+{
+ final SqlNode fromClause;
+ final Span s;
+}
+{
+ <FROM> {
+ s = span();
+ if (!this.conformance.isPipeSyntaxAllowed()) {
+ throw SqlUtil.newContextException(getPos(),
+ RESOURCE.pipeSyntaxNotAllowed());
+ }
+ }
+ fromClause = FromClause()
+ // Report helpful error messages for common mistakes. (Generally, FROM
+ // must be followed by pipe operators.)
+ [
+ LOOKAHEAD(1)
+ (
+ <WHERE> {
+ throw SqlUtil.newContextException(getPos(),
+ RESOURCE.pipeClauseNotAllowed("WHERE", "|> WHERE"));
+ }
+ |
+ <ORDER> {
+ throw SqlUtil.newContextException(getPos(),
+ RESOURCE.fromQueryClauseNotAllowed("ORDER BY"));
+ }
+ |
+ <LIMIT> {
+ throw SqlUtil.newContextException(getPos(),
+ RESOURCE.fromQueryClauseNotAllowed("LIMIT"));
+ }
+ |
+ <OFFSET> {
+ throw SqlUtil.newContextException(getPos(),
+ RESOURCE.fromQueryClauseNotAllowed("OFFSET"));
+ }
+ |
+ <FETCH> {
+ throw SqlUtil.newContextException(getPos(),
+ RESOURCE.fromQueryClauseNotAllowed("FETCH"));
+ }
+ |
+ ( <UNION> | <INTERSECT> | <EXCEPT> | <SET_MINUS> ) {
+ throw SqlUtil.newContextException(getPos(),
+ RESOURCE.fromQueryInSetOpNotAllowed());
+ }
+ )
+ ]
+ { return new SqlFromQuery(s.end(this), fromClause); }
+}
+
+/**
+ * Reads optional pipe operators and applies them to the query {@code e}.
+ *
+ * <p>If {@code with}, {@code e} is a WITH, or an ORDER BY of a WITH, that is
Review Comment:
Reworded it to try to be more clear:
```
/**
* Parses zero or more pipe operators that follow the query {@code e}.
*
* <p>The flag {@code with} signifies whether {@code e} is a WITH that is not
* in parentheses, or an ORDER BY of such a WITH. If so, the operators are
* applied to the body of the WITH, so that they can reference its CTEs.
*/
```
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