USE tpch1;
select cdate from datatypetestm where cdate='';
cdate
select cdatetime from datatypetestm where cdatetime='';
cdatetime
select cdate from datatypetestm where cdate<>'';
cdate
1997-01-01
1997-01-01
1997-01-02
1997-01-03
1997-01-04
2009-12-28
2009-12-29
2009-12-30
2009-12-31
2009-12-31
2009-12-31
select cdatetime from datatypetestm where cdatetime<>'';
cdatetime
1997-01-01 00:00:00
1997-01-01 00:00:01
1997-01-02 00:00:01
1997-01-03 00:00:02
1997-01-04 00:00:03
2009-12-31 23:59:56
2009-12-31 23:59:57
2009-12-31 23:59:58
2009-12-31 23:59:59
2009-12-31 23:59:59
2009-12-31 23:59:59
select * from datatypetestm where cdate=null or cdatetime<>null;
CIDX	CBIGINT	CDECIMAL1	CDECIMAL4	CDECIMAL4_2	CDECIMAL5	CDECIMAL9	CDECIMAL9_2	CDECIMAL10	CDECIMAL18	CDECIMAL18_2	CINTEGER	CSMALLINT	CTINYINT	CDOUBLE	CFLOAT	CDATE	CDATETIME	CCHAR1	CCHAR2	CCHAR3	CCHAR4	CCHAR5	CCHAR6	CCHAR7	CCHAR8	CCHAR9	CCHAR255	CVCHAR1	CVCHAR2	CVCHAR3	CVCHAR4	CVCHAR5	CVCHAR6	CVCHAR7	CVCHAR8	CVCHAR255
select cdate from datatypetestm where cdate is null;
cdate
select cdatetime from datatypetestm where cdatetime is null;
cdatetime
select cdate from datatypetestm where cdate is not null;
cdate
1997-01-01
1997-01-01
1997-01-02
1997-01-03
1997-01-04
2009-12-28
2009-12-29
2009-12-30
2009-12-31
2009-12-31
2009-12-31
select cdatetime from datatypetestm where cdatetime is not null;
cdatetime
1997-01-01 00:00:00
1997-01-01 00:00:01
1997-01-02 00:00:01
1997-01-03 00:00:02
1997-01-04 00:00:03
2009-12-31 23:59:56
2009-12-31 23:59:57
2009-12-31 23:59:58
2009-12-31 23:59:59
2009-12-31 23:59:59
2009-12-31 23:59:59