How to skip/continue delete statement when the table does not exist? - sql

Question

I want to write execute block that I can use for multiple databases with similar structure, some don't have 1 or more tables. I use something like this
execute block as
begin
delete from table1;
delete from table2;
delete from table3;
delete from table4;
delete from table5;
end
and this works for base with all tables, but when table is missing the execute block stops. I want to use this execute block when there is missing table so I don't have to commit the missing one.

Answer 1

You can't do it like this. A table referenced in a delete PSQL statement must exist for the execute block to successfully compile before it can even run.
Instead you will need to use statement blocks containing a execute statement to execute the statements dynamically and a when any exception handler to continue on any error.
For example, something like:
execute block as
begin
begin
execute statement 'delete from table1';
when any do
begin
-- ignore error
end
end
begin
execute statement 'delete from table2';
when any do
begin
-- ignore error
end
end
-- etc
end
You could also check for existence in the system tables before executing the delete dynamically. For example, something like:
execute block
as
declare variable tablename varchar(64);
begin
for select trim(rdb$relation_name)
from rdb$relations
where rdb$relation_name in ('TABLE1', 'TABLE2', 'TABLE3', 'TABLE4', 'TABLE5')
into tablename do
begin
execute statement 'delete from "' || replace(tablename, '"', '""') || '"';
end
end
The table names in the IN-clause must match the name as stored (for unquoted object names like table1 that means uppercase TABLE1). The replace(tablename, '"', '""') is just for completeness to escape possible double quotes in table names.