fix: do not rewrite single columns in derived tables (#11419)

Signed-off-by: Andres Taylor <andres@planetscale.com> Signed-off-by: Andres Taylor <andres@planetscale.com>
vitessio · Oct 3, 2022 · 4342564 · 4342564
1 parent c7116c9
commit 4342564
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Showing 4 changed files with 48 additions and 5 deletions.
diff --git a/go/vt/sqlparser/ast_rewriting.go b/go/vt/sqlparser/ast_rewriting.go
@@ -541,6 +541,14 @@ func (er *astRewriter) unnestSubQueries(cursor *Cursor, subquery *Subquery) {
 	if !ok {
 		return
 	}
+	_, isColName := expr.Expr.(*ColName)
+	if isColName {
+		// If we find a single col-name in a `dual` subquery, we can be pretty sure the user is returning a column
+		// already projected.
+		// `select 1 as x, (select x)`
+		// is perfectly valid - any aliased columns to the left are available inside subquery scopes
+		return
+	}
 	er.bindVars.NoteRewrite()
 	// we need to make sure that the inner expression also gets rewritten,
 	// so we fire off another rewriter traversal here

diff --git a/go/vt/sqlparser/ast_rewriting_test.go b/go/vt/sqlparser/ast_rewriting_test.go
@@ -96,6 +96,10 @@ func TestRewrites(in *testing.T) {
 		in:       "select (select database() from dual) from dual",
 		expected: "select :__vtdbname as `(select database() from dual)` from dual",
 		db:       true,
+	}, {
+		// don't unnest solo columns
+		in:       "select 1 as foobar, (select foobar)",
+		expected: "select 1 as foobar, (select foobar from dual) from dual",
 	}, {
 		in:       "select id from user where database()",
 		expected: "select id from user where database()",

diff --git a/go/vt/vtgate/planbuilder/physical/filter.go b/go/vt/vtgate/planbuilder/physical/filter.go
@@ -37,11 +37,6 @@ func (f *Filter) TableID() semantics.TableSet {
 	return f.Source.TableID()
 }
 
-// PushPredicate implements the PhysicalOperator interface
-func (f *Filter) PushPredicate(expr sqlparser.Expr, semTable *semantics.SemTable) error {
-	panic("unimplemented")
-}
-
 // UnsolvedPredicates implements the PhysicalOperator interface
 func (f *Filter) UnsolvedPredicates(semTable *semantics.SemTable) []sqlparser.Expr {
 	panic("implement me")

diff --git a/go/vt/vtgate/planbuilder/testdata/select_cases.txt b/go/vt/vtgate/planbuilder/testdata/select_cases.txt
@@ -7694,3 +7694,39 @@ Gen4 error: unsupported: JOIN not supported between derived tables
     "user.music"
   ]
 }
+
+# Earlier columns are in scope in subqueries https://github.com/vitessio/vitess/issues/11246
+"SELECT 1 as x, (SELECT x)"
+{
+  "QueryType": "SELECT",
+  "Original": "SELECT 1 as x, (SELECT x)",
+  "Instructions": {
+    "OperatorType": "Route",
+    "Variant": "Reference",
+    "Keyspace": {
+      "Name": "main",
+      "Sharded": false
+    },
+    "FieldQuery": "select 1 as x, (select x from dual where 1 != 1) from dual where 1 != 1",
+    "Query": "select 1 as x, (select x from dual) from dual",
+    "Table": "dual"
+  }
+}
+{
+  "QueryType": "SELECT",
+  "Original": "SELECT 1 as x, (SELECT x)",
+  "Instructions": {
+    "OperatorType": "Route",
+    "Variant": "Reference",
+    "Keyspace": {
+      "Name": "main",
+      "Sharded": false
+    },
+    "FieldQuery": "select 1 as x, (select x from dual where 1 != 1) from dual where 1 != 1",
+    "Query": "select 1 as x, (select x from dual) from dual",
+    "Table": "dual"
+  },
+  "TablesUsed": [
+    "main.dual"
+  ]
+}