Transactions in Informix dbaccess here document approach - informix

Question

I am writing a shell script that invokes dbaccess.
I would like to begin a transaction, do some stuff (e.g. call some procedures) and then make a decision and either commit or rollback the current work. Is this possible?
Here's an example of what I am trying to accomplish
#!/bin/bash
v_value
dbaccess $DB - << SQL
unload to "abc.csv"
select value from table1 where id=1;
SQL
IFS=$'|' arr=( $(awk -F, -v OFS='\n' '{$1=$1}1' abc.csv) )
v_value=${arr[0]}
dbaccess $DB - << SQL
begin;
execute procedure progname();
-- here check everything is ok (e.g. using the previously retrieved $v_value) and either commit or rollback
-- commit|rollback
SQL

Answer 1

You probably want to use the DBACCNOIGN environment variable, which makes DB-Access pay attention to failing statements — and stop. If that's set and you start a transaction, and then a statement within the transaction fails, DB-Access will terminate, which means the transaction will be rolled back.
For example:
$ DBACCNOIGN=1 dbaccess stores - <<'EOF'
> begin work;
> create table anything (num INT NOT NULL, str VARCHAR(20) NOT NULL);
> insert into anything values(1, "one");
> select * from abelone;
> insert into anything values(2, "two");
> select * from anything;
> commit work;
> EOF
Database selected.
Started transaction.
Table created.
1 row(s) inserted.
206: The specified table (abelone) is not in the database.
111: ISAM error: no record found.
Error in line 1
Near character position 21
377: Must terminate transaction before closing database.
853: Current transaction has been rolled back due to error
or missing COMMIT WORK.
$ dbaccess stores - <<'EOF'
> begin work;
> create table anything (num INT NOT NULL, str VARCHAR(20) NOT NULL);
> insert into anything values(1, "one");
> select * from abelone;
> insert into anything values(2, "two");
> select * from anything;
> commit work;
> EOF
Database selected.
Started transaction.
Table created.
1 row(s) inserted.
206: The specified table (abelone) is not in the database.
111: ISAM error: no record found.
Error in line 1
Near character position 21
1 row(s) inserted.
num str
1 one
2 two
2 row(s) retrieved.
Data committed.
Database closed.
$
I then had to use DB-Access again to drop the table Anything that was created.
The value that DBACCNOIGN is set to doesn't matter very much; setting it to 0 or 1 or an empty string all worked equally well.
This is a limited facility; you don't have programmatic control over whether to ignore the error from any given statement. You either abandon ship on the first error or you continue to the end regardless of errors.
You could consider the 'real' SQLCMD program (rather than Microsoft's johnny-come-lately) which is available from the IIUG (International Informix User Group) Software Archive. It allows you to control whether errors from any given group of statements are ignored or not. However, it does not give you full flow control — you can't conditionally execute statements.

Answer 2

Maybe you able to commit/rollback inside of a procedure for this.
But the way you wrote your script, I don't consider necessary create a procedure for that , you can solve using shell script :
#!/bin/bash
v_value=""
dbaccess $DB - << SQL
unload to "abc.csv"
select value from table1 where id=1;
SQL
IFS=$'|' arr=( $(awk -F, -v OFS='\n' '{$1=$1}1' abc.csv) )
v_value=${arr[0]}
{
echo "
begin work;
execute procedure progname();
"
if [ "$v_value" = "1" ] ; then
echo "commit ;"
else
echo "rollback;"
fi;
} | dbaccess $DB -
PLUS
About the "unload" , just as suggestion (I don't like use unload for this kind of script) :
v_value=$( echo "select first 1 value from table1 where id=1;" | dbaccess $DB 2>/dev/null | egrep -v '^ *$|^ *value" | awk '{print $1}')
USING PROCEDURE
If you want avoid use shell script and keep all into SQL code, you will need create a specific procedure for that , something like :
create table test( desc char(10) ) ;
--drop procedure commit_rollback ;
create procedure commit_rollback()
define x int ;
select count(*) into x from test ;
if x > 5 then
commit work;
else
rollback work ;
end if ;
end procedure ;
begin work ;
insert into test values ( '111') ;
insert into test values ( '222') ;
insert into test values ( '333') ;
insert into test values ( '444') ;
insert into test values ( '555') ;
execute procedure commit_rollback() ;
select * from test ;
begin work;
insert into test values ( '111') ;
insert into test values ( '222') ;
insert into test values ( '333') ;
insert into test values ( '444') ;
insert into test values ( '555') ;
insert into test values ( '666') ;
execute procedure commit_rollback() ;
select * from test ;
The code above will have this output
desc
desc
111
222
333
444
555
666