Preserve select order within MySQL UNION?

It’s a good choice to use CASE statement. Do not use UNION. Let us first create a table −

mysql> create table DemoTable    (    Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,    ShippingDate datetime    ); Query OK, 0 rows affected (0.63 sec)

Insert some records in the table using insert command −

mysql> insert into DemoTable(ShippingDate) values('2019-04-21'); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable(ShippingDate) values('2019-01-01'); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable(ShippingDate) values('2019-05-11'); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable(ShippingDate) values('2018-12-31'); Query OK, 1 row affected (0.18 sec) mysql> insert into DemoTable(ShippingDate) values('2019-02-18'); Query OK, 1 row affected (0.19 sec)

Display all records from the table using select statement −

mysql> select *from DemoTable;

This will produce the following output −

+----+---------------------+ | Id | ShippingDate | +----+---------------------+ | 1 | 2019-04-21 00:00:00 | | 2 | 2019-01-01 00:00:00 | | 3 | 2019-05-11 00:00:00 | | 4 | 2018-12-31 00:00:00 | | 5 | 2019-02-18 00:00:00 | +----+---------------------+ 5 rows in set (0.00 sec)

Following is the query to preserve select order using order by case.

mysql> select *from DemoTable ORDER BY CASE WHEN ShippingDate < CURDATE() THEN ShippingDate ELSE CURDATE() END DESC, ShippingDate ASC;

This will produce the following output −

+----+---------------------+ | Id | ShippingDate | +----+---------------------+ | 3 | 2019-05-11 00:00:00 | | 1 | 2019-04-21 00:00:00 | | 5 | 2019-02-18 00:00:00 | | 2 | 2019-01-01 00:00:00 | | 4 | 2018-12-31 00:00:00 | +----+---------------------+ 5 rows in set (0.00 sec)