What is the sum of total pounds of purchase in year 2018 for all branches in London?
CREATE TABLE purchase (
    branch_id VARCHAR,
    year VARCHAR
)

CREATE TABLE branch (
    branch_id VARCHAR,
    city VARCHAR
)
SELECT SUM(total_pounds) FROM purchase AS T1 JOIN branch AS T2 ON T1.branch_id = T2.branch_id WHERE T2.city = 'London' AND T1.year = 2018
Below are sql tables schemas paired with instruction that describes a task. Using valid SQLite, write a response that appropriately completes the request for the provided tables. ### Instruction: What is the sum of total pounds of purchase in year 2018 for all branches in London? ### Input: CREATE TABLE purchase (
    branch_id VARCHAR,
    year VARCHAR
)

CREATE TABLE branch (
    branch_id VARCHAR,
    city VARCHAR
) ### Response: SELECT SUM(total_pounds) FROM purchase AS T1 JOIN branch AS T2 ON T1.branch_id = T2.branch_id WHERE T2.city = 'London' AND T1.year = 2018