By introducing an explicit "AS" to set output names in the SELECT column
list, there are no issues with reserved names. Unfortunately, this
happened on PostgreSQL in the older version 13 with the reserved name
"name". Adding "AS" mitigates this issue.
Furthermore, I have put each column name in its own line for the SELECT
queries to ease the readability of the query itself and of future diffs.
Fixes#884.
Historical data from an older Icinga 2 installation contained NULL
values for the name column in some rows of the icinga_commenthistory and
icinga_downtimehistory tables.
Normally this field contains something like
${name1}!${name2}!${unique_value} where the $unique_value is based on a
timestamp for older entries and a UUID for newer ones. For a concrete
example, this could be "host.example.com!ping6!123…".
Unfortunately, using an empty string for these NULL values will cause an
error later because the new primary key will be calculated based on it.
Therefore, a new deterministic name is generated based on the primary
keys and the known name1 and name2 values.
Closes#766.
