MySQL: Select with first and last day of previous month - mysql

Question

Using PhpMyadmin, I have this sentence working:
SELECT id_order as Ref FROM t_orders WHERE DATE(invoice_date) = CURDATE()
Now I want to reemplace "current date" (CURDATE) for the first day of previous month in advance.
The answer of Ankit Bajpai solved my problem (thank you):
SELECT id_order as Ref FROM t_orders WHERE DATE(invoice_date) >= concat(date_format(LAST_DAY(now() - interval 1 month),'%Y-%m-'),'01');

Answer 1

in MYSQL you can try the below
First day of Previous Month
select last_day(curdate() - interval 2 month) + interval 1 day
Last day of Previous Month
select last_day(curdate() - interval 1 month)
First day of Current Month
select last_day(curdate() - interval 1 month) + interval 1 day
Last day of Current Month
select last_day(curdate())

Answer 2

Try following query:-
SELECT id_order as Ref
FROM t_orders
WHERE DATE(invoice_date) >= concat(date_format(LAST_DAY(now() - interval 1 month),'%Y-%m-'),'01');

Answer 3

For MS SQL Server:
DECLARE #firstDayOfLastMonth DATETIME = DATEADD(MONTH, -1, DATEADD(MONTH, DATEDIFF(MONTH, 0, GETDATE()), 0))
DECLARE #lastDayOfLastMonth DATETIME = DATEADD(DAY, -1, DATEADD(MONTH, DATEDIFF(MONTH, 0, GETDATE()), 0))
SELECT #firstDayOfLastMonth;
SELECT #lastDayOfLastMonth;

Answer 4

After reading closely... you want the entire month, of the previous month. You can do this:
SELECT id_order as Ref FROM t_orders
WHERE
DATE(invoice_date) >= DATEADD(MONTH, DATEDIFF(MONTH, 0, GETDATE())-1, 0)
AND
DATE(invoice_date) <= DATEADD(month, DATEDIFF(MONTH, 0, GETDATE()), -1)
OR
SELECT id_order as Ref FROM t_orders
WHERE
MONTH(DATE(invoice_date)) = MONTH(DATEADD(MONTH,-1,GETDATE()))