17. union 和 order by

[伟洪winni]

$sql  = '';
$sql .= "(select * from tbl_zteach_evaluation where  fld_startmission < now() and fld_endevaluate > now() order by fld_endevaluate desc) union ";
$sql .= "(select * from tbl_zteach_evaluation where  fld_startmission > now() order by fld_endevaluate asc) union ";
$sql .= "(select * from tbl_zteach_evaluation where  fld_endevaluate < now() order by fld_endevaluate desc) ";

order by 不能正确排序

[伟洪winni]

百度的时候有看到这种写法, 我试了不可以用, 和我的环境有关?

[伟洪winni]

[xuzuning]

虽然你用了括号，但是 MySQL 并不会去理睬他 联合（union）查询只有最后的 order by 有效 至少要写成这样

select * from (select * from tbl_zteach_evaluation where  fld_startmission < now() and fld_endevaluate > now() order by fld_endevaluate desc) a
union
select * from (select * from tbl_zteach_evaluation where  fld_startmission > now() order by fld_endevaluate asc) b 
union
select * from (select * from tbl_zteach_evaluation where  fld_endevaluate < now() order by fld_endevaluate desc) c

[伟洪winni]