MySQL 8.0

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CREATE TABLE opportunities
(close_date DATE NOT NULL,
sale_amount DECIMAL NOT NULL);

INSERT INTO opportunities VALUES ('20190101',100);
INSERT INTO opportunities VALUES ('20190115',115);
INSERT INTO opportunities VALUES ('20190210',150);
INSERT INTO opportunities VALUES ('20190212',180);
INSERT INTO opportunities VALUES ('20190306',200);
INSERT INTO opportunities VALUES ('20190315',220);
INSERT INTO opportunities VALUES ('20190422',250);
INSERT INTO opportunities VALUES ('20190428',260);
INSERT INTO opportunities VALUES ('20190509',300);
INSERT INTO opportunities VALUES ('20190521',310);
INSERT INTO opportunities VALUES ('20190601',325);
INSERT INTO opportunities VALUES ('20190630',375);
INSERT INTO opportunities VALUES ('20190703',400);
INSERT INTO opportunities VALUES ('20190716',500);
INSERT INTO opportunities VALUES ('20190813',550);
INSERT INTO opportunities VALUES ('20190814',575);
INSERT INTO opportunities VALUES ('20190909',625);
INSERT INTO opportunities VALUES ('20190929',650);
INSERT INTO opportunities VALUES ('20191004',700);
INSERT INTO opportunities VALUES ('20191022',750);
INSERT INTO opportunities VALUES ('20191112',800);
INSERT INTO opportunities VALUES ('20191119',900);
INSERT INTO opportunities VALUES ('20191202',950);
INSERT INTO opportunities VALUES ('20191216',975);

close_month	sale_amount
2019-01-01	215
2019-02-01	545
2019-03-01	965
2019-04-01	1475
2019-05-01	2085
2019-06-01	2785
2019-07-01	3470
2019-08-01	4265
2019-09-01	5120
2019-10-01	6060
2019-11-01	7150
2019-12-01	8375