Go Forward and Backward in AST

[vnnv01]

Hi All,

I have query which I wanted to convert from one database syntax to another.

Query 1: Select a+b as c ,a, b from test where c=100;

This query from teradata will not work in Postgres.

So I have to convert the query to

Output: Select a,b,c from (select a,b, a+b as c from test ) test where c=100;

I have created grammar rules to parse this rules.

K_SELECT - - Select
Select_List -- a,b,a+b as c
K_FROM - From
From_Clause -- test
where_clause - c=100.

I Parse the sql and uses match to match a rule and use a function for that rule to do transformation.

let mut s = String::new();
for i in sql_parse.into_inner() {
match i.as_rule() {
Rule::K_SELECT => { s.push_str(select_function(&i)) },
Rule::K_FROM => { s.push_str(from_function(&i)) },
Rule::select_list => {s.push_str(select_list_function(&i)) },
Rule::from_clause => {s.push_str(from_clause_function(&i))},
Rule::where_clause => {s.push_str(where_clause_function(&i))}
}

Now in the function select_function I might need to access the Pair for the Rule::where_clause and in sometimes I want to get access to select_list rule values from where_clause.

How to move back and forth in tree from the current position. Like when I am in where_clause_function, I should be able to access the select_list rule.

Thanks