How about this problem

[Chen Bo]

MYSQL version:4.1.2

INSERT INTO T_M_CATEGORY_SEN
(RBID, CATE6_DIV, LOCALCATEID, CONSOLICATEID, EXP_DATE_FROM, EXP_DATE_TO,
CREATE_USER, CREATE_DATE, UPDATE_USER, UPDATE_DATE, GENEID)
SELECT e.RBID, 1, d.LOCALCATEID, d.CONSOLICATEID, d.EXP_DATE_FROM, d.EXP_DATE_TO,
d.CREATE_USER, d.CREATE_DATE, d.UPDATE_USER, d.UPDATE_DATE, d.GENEID
FROM (SELECT * FROM T_M_CONSOLICATE a, T_M_LOCALCATE b, T_M_6DIGIT2 c
WHERE a.CON_CATE_CODE = b.LOC_CATE_CODE and c.CATE6_CODE = a.CON_CATE_CODE) d,
(SELECT RBID FROM T_M_REGIONB) e
WHERE NOT EXISTS
(SELECT * FROM T_M_CATEGORY_SEN f WHERE
d.LOCALCATEID = f.LOCALCATEID and d.CONSOLICATEID = f.CONSOLICATEID
AND e.RBID = f.RBID
group by f.LOCALCATEID, f.CONSOLICATEID);

When the SQL running:sometimes running 2 hours,but sometimes running only 1 minute.
And user command "show processlist":
When running 2 hours:State is "Sending data"
When running 1 minute:State first is "Sending data"(about 5 seconds),then change to "Copying to tmp table"

explain the SQL,there are some messages bellow:

id,"select_type","table","type",possible_keys,key,key_len,ref,rows,"Extra"
1,"PRIMARY","<derived2>","ALL",NULL,NULL,NULL,NULL,377,""
1,"PRIMARY","<derived3>","ALL",NULL,NULL,NULL,NULL,91,"Using where"
4,"DEPENDENT SUBQUERY","f","ref","T_M_CATEGORY_SEN_FK1,T_M_CATEGORY_SEN_FK2","T_M_CATEGORY_SEN_FK1",5,"d.LOCALCATEID",69,"Using where; Using temporary; Using filesort"
3,"DERIVED","T_M_REGIONB","index",NULL,"PRIMARY",4,NULL,91,"Using index"
2,"DERIVED","c","ALL",NULL,NULL,NULL,NULL,321,""
2,"DERIVED","a","ALL",NULL,NULL,NULL,NULL,3649,"Using where"
2,"DERIVED","b","ALL",NULL,NULL,NULL,NULL,3653,"Using where"


Why the SQL sometines running slow or fast?

Who can help me?Thank you very much!