Export results from DB2 to CSV including column names via bash - bash

Question

This question branches off a question already asked.
I want to make a csv file with the db2 results including column names.
EXPORT TO ...
SELECT 1 as id, 'COL1', 'COL2', 'COL3' FROM sysibm.sysdummy1
UNION ALL
(SELECT 2 as id, COL1, COL2, COL3 FROM myTable)
ORDER BY id
While this does work, I am left with an unwanted column and rows of 1 and 2's
Is there a way to do this via the db2 command or a full bash alternative without redundant columns while keeping the header at the top?
e.g.
Column 1 Column 2 Column 3
data 1 data 2 data3
... ... ...
instead of:
1 Column 1 Column 2 Column 3
2 data 1 data 2 data3
2 ... ... ...

Answer 1

All the answers I've seen use two separate export statements. The first generates the column headers:
db2 "EXPORT TO /tmp/header.csv of del
SELECT
SUBSTR(REPLACE(REPLACE(XMLSERIALIZE(CONTENT XMLAGG(XMLELEMENT(NAME c,colname)
ORDER BY colno) AS VARCHAR(1500)),'<C>',', '),'</C>',''),3)
FROM syscat.columns WHERE tabschema=${SCHEMA} and tabname=${TABLE}"
then the query body
db2 "EXPORT TO /tmp/body.csv of del
SELECT * FROM ${SCHEMA}.${TABLE}"
then
cat /tmp/header.csv /tmp/body.csv > ${TABLE}.csv

Answer 2

If you just want the headers for the extracted data and you want those headers to always be on top and you want to be able to change the names of those headers so it appears more user-friendly and put it all into a CSV file.
You can do the following:
# Creates headers and new output file
HEADERS="ID,USERNAME,EMAIL,ACCOUNT DISABLED?"
echo "$HEADERS" > "$OUTPUT_FILE"
# Gets results from database
db2 -x "select ID, USERNAME, DISABLED FROM ${SCHEMA}.USER WHERE lcase(EMAIL)=lcase('$USER_EMAIL')" | while read ID USERNAME DISABLED ;
do
# Appends result to file
echo "${ID},${USERNAME},${USER_EMAIL},${DISABLED}" >> "$OUTPUT_FILE"
done
No temporary files or merging required.

Answer 3

Db2 for Linux/Unix/Windows lacks a (long overdue) simple opting (to the export command) for this common requirement.
But using the bash shell you can run two separate exports (one for the column-headers, the other for the data ) and concat the results to a file via an intermediate named pipe.
Using an intermediate named pipe means you don't need two flat-file copies of the data.
It is ugly and awkward but it works.
Example fragment (you can initialize the variables to suit your environment):
mkfifo ${target_file_tmp}
(( $? != 0 )) && print "\nERROR: failed to create named pipe ${target_file_tmp}" && exit 1
db2 -v "EXPORT TO ${target_file_header} of del SELECT 'COL1', 'COL2', 'COL3' FROM sysibm.sysdummy1 "
cat ${target_file_header} ${target_file_tmp} >> ${target_file} &
(( $? > 0 )) && print "Failed to append ${target_file} . Check permissions and free space" && exit 1
db2 -v "EXPORT TO ${target_file_tmp} of del SELECT COL1, COL2, COL3 FROM myTable ORDER BY 1 "
rc=$?
(( rc == 1 )) && print "Export found no rows matching the query" && exit 1
(( rc == 2 )) && print "Export completed with warnings, your data might not be what you expect" && exit 1
(( rc > 2 )) && print "Export failed. Check the messages from export" && exit 1

Answer 4

This would work for your simple case
EXPORT TO ...
SELECT C1, C2, C3 FROM (
SELECT 1 as id, 'COL1' as C1, 'COL2' as C2, 'COL3' as C3 FROM sysibm.sysdummy1
UNION ALL
(SELECT 2 as id, COL1, COL2, COL3 FROM myTable)
)
ORDER BY id
Longer term, EXTERNAL TABLE support (already in Db2 Warehouse) which has the INCLUDEHEADER option is (I guess) going to appear in Db2 at some point.

Answer 5

I wrote a stored procedure that extracts the header via describe command. The names can be retrieved from a temporary table, and be exported to a file. The only thing it is still not possible is to concatenate the files via SQL, thus a cat to both file and redirection to another file is necessary as last step.
CALL DBA.GENERATE_HEADERS('SELECT * FORM SYSCAT.TABLES') #
EXPORT TO myfile_header OF DEL SELECT * FROM SESSION.header #
EXPORT TO myfile_body OF DEL SELECT * FORM SYSCAT.TABLES #
!cat myfile_header myfile_body > myfile #
The code of the stored procedure is at: https://gist.github.com/angoca/8a2d616cd1159e5d59eff7b82f672b72
More information at: https://angocadb2.blogspot.com/2019/11/export-headers-of-export-in-db2.html.