Format VARCHAR amounts into $ with M/B suffix

You are given a table transactions with:

• id (primary key)
• amount_str (VARCHAR): a numeric string representing an amount in dollars (e.g., '950' , '2500000' , '9876543210' ).

Task (SQL): Write a query that outputs id and a formatted amount string:

• If amount < 1,000,000 : output like $950 (no suffix).
• If 1,000,000 <= amount < 1,000,000,000 : output as dollars in millions with suffix M , rounded to 1 decimal (e.g., 2500000 -> $2.5M ).
• If >= 1,000,000,000 : output as dollars in billions with suffix B , rounded to 1 decimal (e.g., 9876543210 -> $9.9B ).

Assume amount_str may contain leading/trailing spaces; you should convert it to a numeric type before comparing/dividing.