Sum columns corresponding values according to similar dates in MySQL?

For this, use aggregate function SUM() along with GROUP BY. Let us first create a table −

mysql> create table DemoTable1522
   -> (
   -> ProductPurchaseDate date,
   -> NumberOfProduct int
   -> );
Query OK, 0 rows affected (1.51 sec)

Insert some records in the table using insert command −

mysql> insert into DemoTable1522 values('2019-01-21',45);
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable1522 values('2018-12-31',78);
Query OK, 1 row affected (0.12 sec)
mysql> insert into DemoTable1522 values('2019-01-21',67);
Query OK, 1 row affected (0.12 sec)
mysql> insert into DemoTable1522 values('2019-03-01',56);
Query OK, 1 row affected (0.19 sec)
mysql> insert into DemoTable1522 values('2018-01-21',97);
Query OK, 1 row affected (0.10 sec)
mysql> insert into DemoTable1522 values('2019-01-21',47);
Query OK, 1 row affected (0.15 sec)

Display all records from the table using select statement −

mysql> select * from DemoTable1522;

This will produce the following output −

+---------------------+-----------------+
| ProductPurchaseDate | NumberOfProduct |
+---------------------+-----------------+
| 2019-01-21          |              45 |
| 2018-12-31          |              78 |
| 2019-01-21          |              67 |
| 2019-03-01          |              56 |
| 2018-01-21          |              97 |
| 2019-01-21          |              47 |
+---------------------+-----------------+
6 rows in set (0.00 sec)

Following is the query to count columns according to dates in MySQL −

mysql> select ProductPurchaseDate,sum(NumberOfProduct) from DemoTable1522
   -> group by ProductPurchaseDate;

This will produce the following output −

+---------------------+----------------------+
| ProductPurchaseDate | sum(NumberOfProduct) |
+---------------------+----------------------+
| 2019-01-21          |                  159 |
| 2018-12-31          |                   78 |
| 2019-03-01          |                   56 |
| 2018-01-21          |                   97 |
+---------------------+----------------------+
4 rows in set (0.00 sec)