Fix incorrect variable substitution for column references in PL/pgSQL

This commit addresses issue #2354 where field names matching parameter or
variable names inside a PL/pgSQL function were incorrectly substituted
by the interpreter when used as part of a table alias or record (e.g. c.id).
By checking if a token is preceded by a dot (.), we can accurately
skip variable substitution for field identifiers.

Author: test

server/plpgsql/statements.go

@@ -471,25 +471,31 @@ func substituteVariableReferences(expression string, stack *InterpreterStack) (n
 		token := scanResult.Tokens[i]
 		substring := expression[token.Start:token.End]
 		// varMap lowercases everything, so we'll lowercase our substring to enable case-insensitivity
-		if _, ok := varMap[strings.ToLower(substring)]; ok {
-			// If there's a '.', then we'll assume this is accessing a record's field (`NEW.val1` for example)
-			for i+2 < len(scanResult.Tokens) && scanResult.Tokens[i+1].Token == '.' {
-				nextFieldSubstring := expression[scanResult.Tokens[i+2].Start:scanResult.Tokens[i+2].End]
-				substring += "." + nextFieldSubstring
-				i += 2
-			}
-			// Variables cannot have a '(' after their name as that would classify them as functions, so we have to
-			// explicitly check for that. This is because variables and functions can share names, for example:
-			// SELECT COUNT(*) INTO count FROM table_name;
-			if i+1 >= len(scanResult.Tokens) || scanResult.Tokens[i+1].Token != '(' {
+		isAfterDot := i > 0 && scanResult.Tokens[i-1].Token == '.'
+
+		if !isAfterDot {
+			if _, ok := varMap[strings.ToLower(substring)]; ok {
+				// If there's a '.', then we'll assume this is accessing a record's field (`NEW.val1` for example)
+				for i+2 < len(scanResult.Tokens) && scanResult.Tokens[i+1].Token == '.' {
+					nextFieldSubstring := expression[scanResult.Tokens[i+2].Start:scanResult.Tokens[i+2].End]
+					substring += "." + nextFieldSubstring
+					i += 2
+				}
+				// Variables cannot have a '(' after their name as that would classify them as functions, so we have to
+				// explicitly check for that. This is because variables and functions can share names, for example:
+				// SELECT COUNT(*) INTO count FROM table_name;
+				if i+1 >= len(scanResult.Tokens) || scanResult.Tokens[i+1].Token != '(' {
+					referencedVars = append(referencedVars, substring)
+					newExpression += fmt.Sprintf("$%d ", len(referencedVars))
+				} else {
+					newExpression += substring + " "
+				}
+			} else if _, ok := triggerSpecialVariables[substring]; ok {
 				referencedVars = append(referencedVars, substring)
 				newExpression += fmt.Sprintf("$%d ", len(referencedVars))
 			} else {
 				newExpression += substring + " "
 			}
-		} else if _, ok := triggerSpecialVariables[substring]; ok {
-			referencedVars = append(referencedVars, substring)
-			newExpression += fmt.Sprintf("$%d ", len(referencedVars))
 		} else {
 			newExpression += substring + " "
 		}

testing/go/create_function_plpgsql_test.go

@@ -704,6 +704,40 @@ $$ LANGUAGE plpgsql;`},
 				},
 			},
 		},
+		{
+			Name: "RETURNS TABLE with conflicting variable names",
+			SetUpScript: []string{
+				`CREATE TABLE customers2 (
+					id INT PRIMARY KEY,
+					name TEXT
+				);`,
+				`INSERT INTO customers2 VALUES (1, 'John'), (2, 'Jane');`,
+				`CREATE OR REPLACE FUNCTION func_conflict(n INT) RETURNS TABLE (id INT, name TEXT) 
+					LANGUAGE plpgsql
+					AS $$
+					BEGIN
+						RETURN QUERY
+						SELECT c.id, c.name
+						FROM customers2 c
+						WHERE c.id = n;
+					END;
+					$$;`,
+			},
+			Assertions: []ScriptTestAssertion{
+				{
+					Query: "SELECT func_conflict(1);",
+					Expected: []sql.Row{
+						{"(1,John)"},
+					},
+				},
+				{
+					Query: "SELECT func_conflict(2);",
+					Expected: []sql.Row{
+						{"(2,Jane)"},
+					},
+				},
+			},
+		},
 		{
 			Name: "RETURNS SETOF with composite param",
 			SetUpScript: []string{