opt: cast inlined constant to the variable's type in InlineConstVar

pkg/sql/opt/norm/inline_funcs.go

@@ -388,6 +388,16 @@ func (c *CustomFuncs) InlineConstVar(f memo.FiltersExpr) memo.FiltersExpr {
 	replace = func(nd opt.Expr) opt.Expr {
 		if t, ok := nd.(*memo.VariableExpr); ok {
 			if e, ok := vals[t.Col]; ok {
+				// The constant was matched against the variable using Equivalent
+				// (not Identical) above, so its type may differ from the
+				// variable's (e.g. a STRING constant for a NAME column).
+				// Substituting the constant directly would change the result of
+				// type-sensitive expressions such as pg_typeof, so cast the
+				// constant to the variable's type when the two are not identical.
+				colType := c.mem.Metadata().ColumnMeta(t.Col).Type
+				if !e.DataType().Identical(colType) {
+					return c.f.ConstructCast(e, colType)
+				}
 				return e
 			}
 		}

pkg/sql/opt/norm/testdata/rules/inline

@@ -226,6 +226,27 @@ project
                 │              └── true [as=column14:14]
                 └── false
 
+# Regression test for #170544. InlineConstVar must not replace a variable with a
+# constant whose type is equivalent but not identical to the variable's type
+# without a cast, since that changes the result of type-sensitive expressions
+# such as pg_typeof. Here n is NAME and the constant 'hello' is STRING; the
+# inlined constant is cast back to NAME so pg_typeof(n) still reports 'name' and
+# the row is not incorrectly filtered out.
+exec-ddl
+CREATE TABLE t_name (n NAME)
+----
+
+norm expect=InlineConstVar
+SELECT * FROM t_name WHERE n = 'hello' AND pg_typeof(n)::TEXT = 'name'
+----
+select
+ ├── columns: n:1!null
+ ├── fd: ()-->(1)
+ ├── scan t_name
+ │    └── columns: n:1
+ └── filters
+      └── n:1 = 'hello' [outer=(1), constraints=(/1: [/'hello' - /'hello']; tight), fd=()-->(1)]
+
 # --------------------------------------------------
 # InlineProjectConstants
 # --------------------------------------------------