SQL uses a union sorting problem

Original: 65628037

The recent union query using SQL statements, surprised to find: SQL is not a problem, the union query is not a problem, you can get the desired results, but in the order of the results, but there is a problem.

1.UNION Query No problem

2. SELECT ' id ', 'username ',' mobile ',' time ',ID as leader
4. from ' Grouporder_leader '
6. WHERE ' courseid ' = + ' merchid ' = All and ' status ' = 1
8. UNION All
10. SELECT Leadorderid,username,mobile, time,null
12. from ' Grouporder_partner '
14. WHERE courseid=and status=1 and merchid=

The results are as follows

2. The sorting is going to be a problem.

2. SELECT ' id ', 'username ',' mobile ',' time ',ID as leader
4. from ' Grouporder_leader '
6. WHERE ' courseid ' = + ' merchid ' = All and ' status ' = 1
8. ORDER by Time DESC
10. UNION All
12. SELECT Leadorderid,username,mobile, time,null
14. from ' Grouporder_partner '
16. WHERE courseid=and status=1 and merchid=
18. ORDER by Time DESC

Error after executing this SQL statement.

3. Create a temporary table

Save the query results using a method similar to creating a temporary table, and then sort the query on the staging table.

2. SELECT id,username,mobile,time,leader
4. From (SELECT ' id ', 'username ', 'mobile ',' time ',ID as leader
6. from ' Grouporder_leader ' WHERE ' courseid ' = + ' merchid ' = All and ' st ATUs ' = 1
8. UNION All
10. SELECT Leadorderid,username,mobile, time,null
12. from ' Grouporder_partner ' WHERE courseid=and status=1 and merchid=
14. )
16. ORDER by Time DESC

4. Aliases

Do not know why the 3rd step in the query is still not, and then the result of the union query the individual name, and then query the sort is no problem.

2. SELECT A.id,a.username,a.mobile,a.time,a.leader
4. From (SELECT ' id ', 'username ', 'mobile ',' time ',ID as leader
6. from ' Grouporder_leader ' WHERE ' courseid ' = + ' merchid ' = All and ' s Tatus ' = 1
8. UNION All
10. SELECT Leadorderid,username,mobile, time,null
12. from ' Grouporder_partner ' WHERE courseid=and status=1 and merchid= /c11>
14. ) as a
16. ORDER by Time DESC

The result is correct.

Find out to say, and then go to heavy or other operations, also no problem.

2. SELECT DISTINCT a.id,a.username,a.mobile,from_unixtime (a.time,'%y/%m/%d ') as _time,a.leader
4. From (SELECT ' id ', 'username ', 'mobile ',' time ',ID as leader
6. from ' Grouporder_leader ' WHERE ' courseid ' = + ' merchid ' = ' status ' = C10>1
8. UNION All
10. SELECT Leadorderid,username,mobile, time,null
12. from ' Grouporder_partner ' WHERE courseid=and status=1 and merchid=
14. ) as a
16. ORDER by Time DESC

SQL uses a union sorting problem