update doc and test cases again

README.md

@@ -269,13 +269,15 @@ fmt.Println(err)
 And a sample for PostgreSQL. Note that the dollar quote is supported.
 
 ```go
+// Only the last `$1` is interpolated.
+// Others are not interpolated as they are inside dollar quote (the `$$`).
 query, err := PostgreSQL.Interpolate(`
 CREATE FUNCTION dup(in int, out f1 int, out f2 text) AS $$
     SELECT $1, CAST($1 AS text) || ' is text'
 $$
 LANGUAGE SQL;
 
-SELECT * FROM dup(42);`, []interface{}{42, 64})
+SELECT * FROM dup($1);`, []interface{}{42})
 
 fmt.Println(query)
 fmt.Println(err)

flavor_test.go

@@ -148,13 +148,15 @@ func ExampleFlavor_Interpolate() {
 }
 
 func ExampleFlavor_Interpolate_postgreSQL() {
+	// Only the last `$1` is interpolated.
+	// Others are not interpolated as they are inside dollar quote (the `$$`).
 	query, err := PostgreSQL.Interpolate(`
 CREATE FUNCTION dup(in int, out f1 int, out f2 text) AS $$
     SELECT $1, CAST($1 AS text) || ' is text'
 $$
 LANGUAGE SQL;
 
-SELECT * FROM dup(42);`, []interface{}{42, 64})
+SELECT * FROM dup($1);`, []interface{}{42})
 
 	fmt.Println(query)
 	fmt.Println(err)