Is Row format serde a compulsory parameter to be used while creating Hive table - hadoop

Question

I created a temporary hive table on top of textfile like this:
CREATE EXTERNAL TABLE tc (fc String,cno String,cs String,tr String,at String,act String,wa String,dn String,pnm String,rsk String,ttp String,tte String,aml String,pn String,ttn String)
ROW FORMAT DELIMITED
FIELDS TERMINATED BY ‘,’
STORED AS TEXTFILE
location '/home/hbaseuser/tc';
Then I created an ORC table like this:
CREATE EXTERNAL TABLE tc1 (fc String,cno String,cs String,tr String,at String,act String,wa String,dn String,pnm String,rsk String,ttp String,tte String,aml String,pn String,ttn String)
Row format delimited
Fields terminated by '\t'
STORED AS orc
location '/user/hbaseuser/tc1';
Then I used this command to import data to hive table:
insert overwrite table tc1 select * from table tc;
now orc file is available at '/user/hbaseuser/tc1'
and I am able to read from orc table.
my question is what is the use of tag Row format serde 'org.apache.hadoop.hive.contrib.serde2.ORCSerDe'

Answer 1

When ROW FORMAT Serde is specified, it overrides the native Serde and uses that for table creation.
As per documentation,
You can create tables with a custom SerDe or using a native SerDe. A
native SerDe is used if ROW FORMAT is not specified or ROW FORMAT
DELIMITED is specified. Use the SERDE clause to create a table with a
custom SerDe.
STORED AS ORC statement is equivalent to writing
ROW FORMAT SERDE 'org.apache.hadoop.hive.ql.io.orc.OrcSerde'
STORED AS INPUTFORMAT
'org.apache.hadoop.hive.ql.io.orc.OrcInputFormat' OUTPUTFORMAT
'org.apache.hadoop.hive.ql.io.orc.OrcOutputFormat'
You can either use "Stored as" or "Row Format Serde" statement. You can refer the below documentation for more details:
https://cwiki.apache.org/confluence/display/Hive/LanguageManual+DDL#LanguageManualDDL-RowFormats&SerDe
https://cwiki.apache.org/confluence/display/Hive/DeveloperGuide#DeveloperGuide-HiveSerDe