Convert 2 HTML file which is output from SQL query into 1 main HTML output file in shell script

In shell script, I used 2 different SQL query & output of these 2 files in HTML format like (eg- ab.html, cd.html). Before DML operation 1 SQL query will run then after DML operation another query will run. Shell script as ->

#/bin/ksh

ab=$(SQLPLUS -s <username>/<password>@DB <<EOF
set heading ON
set trimspool OFF
SET MARKUP HTML ON
set feedback off
spool ab.html
select col_1, col_2, col_3 from <tab>;
spool off;
exit;
EOF)

echo "$ab" > ab.html

----- DML operation perform

cd=$(SQLPLUS -s <username>/<password>@DB <<EOF
set heading ON
set trimspool OFF
SET MARKUP HTML ON
set feedback off
spool cd.html
select col_4 from <tab>;
spool off;
exit;
EOF)

echo "$cd" > cd.html

cat ab.html cd.html > output.html
exit 0

Then getting output.html file as ->

 ______________________________
| col_1     | col_2  |   col_3 |
| .....     | ...... |   ..... |
| .....     | ...... |   ..... |
|___________|________|_________|
 ______________________________              
|             col_4            |
|             ......           |
|______________________________|

But I want final output.html like col_1, col_2, col_3, col_4 column in one table like below ->

 ______________________________________
| col_1     | col_2  |   col_3  | col_4|
| .....     | ...... |   .....  | .....|
| .....     | ...... |   .....  | .....|
|___________|________|__________|______|

Could you please help me how to merge these 2 HTML file into one output HTML file so that we can able to see like above format. I just draw HTML table as example but internal border always comes in HTML table, so please don't look HTML table format that I used.