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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)
Updated on: 30-Jul-2019
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