Mysql-ask for an SQL statement and its principles. for details, refer to the description!

! If the pid of the order table is null, the primary order needs to be sorted in descending order of the primary order ddate, and the suborder is placed after the primary order! [Image description ((img.ask.csdn.netupload201603231458703376_47054.jpg) the SQL statement I wrote can implement & quot; SELECTDISTINCTidfrom (S... mysqlsql

If the order table pid is null, the primary order is used.
The requirement is to sort the orders in descending order by the primary order ddate. the sub-orders are placed after the primary order.
Final result

The SQL statement I wrote can be implemented.

Select distinct id from (SELECT B. id,. ddate FROM 'tttest'a, 'tttest' B where. id = B. pid union SELECT c. id, c. ddate from tttest c) t order by t. ddate desc, id

However, it is too complicated to find a brief SQL statement.