SQL Server INSERT INTO with WHERE clause

Question

I'm trying to insert some mock payment info into a dev database with this query:

INSERT
    INTO
        Payments(Amount)
    VALUES(12.33)
WHERE
    Payments.CustomerID = '145300';

How can adjust this to execute? I also tried something like this:

IF NOT EXISTS(
    SELECT
        1
    FROM
        Payments
    WHERE
        Payments.CustomerID = '145300' 
) INSERT 
    INTO
        Payments(Amount)
    VALUES(12.33);

Answer 1

I think you are trying to do an update statement (set amount = 12.33 for customer with ID = 145300)

UPDATE Payments
SET Amount = 12.33
WHERE CustomerID = '145300'

Else if you are trying to insert a new row then you have to use

IF NOT EXISTS(SELECT 1 FROM Payments WHERE CustomerID = '145300')
    INSERT INTO Payments(CustomerID,Amount)
    VALUES('145300',12.33)

Or if you want to combine both command (if customer exists do update else insert new row)

IF NOT EXISTS(SELECT 1 FROM Payments WHERE CustomerID = '145300')
    INSERT INTO Payments(CustomerID,Amount)
    VALUES('145300',12.33)
ELSE
    UPDATE Payments
    SET Amount = 12.33
    WHERE CustomerID = '145300'