string update1 = $"UPDATE users SET CashAmount = CashAmount - '{cash}' WHERE Login = '{MinusCash.Text}'";
string update2 = $"UPDATE users SET CashAmount = CashAmount + '{cash}' WHERE Login = '{PlusCash.Text}'";
UPDATE users
SET CashAmount = (CASE
WHEN Login = '{PlusCash.Text}'
THEN (CashAmount + '{cash}')
ELSE (CashAmount - '{cash}')
END)
WHERE Login IN ('{PlusCash.Text}', '{MinusCash.Text}')