Before now table definitions could define collations only for MariaDB using the
MariaDB's collation names directly.
Now instead definitions get a slightly more abstract collation name syntax, but
only supporting the collations utf8mb4_bin and utf8mb4_unicode_(cs|ci) (wrapped
as utf8_bin, utf8_general_(cs|ci)), because those are the ones that have
practical use for GNU social.
Which also means that on MariaDB the formerly used utf8mb4_general_(cs|ci) have
been superseded by utf8mb4_unicode_(cs|ci), as they are the more modern
replacement.
Introduce collation support on PostgreSQL which results in use of the C (POSIX)
collation as utf8_bin and the und-x-icu collation as utf8_general_cs.
utf8_general_ci is also mapped to und-x-icu, which makes it case-sensitive,
unfortunately.
"blob" is practically used with the expectation of unlimited length, which is
true with PostgreSQL's bytea, but not with MariaDB's BLOB, which is limited to
64KiB.
So instead use LONGBLOB, which has a maximum of 4GiB, effectively unlimited.
On PostgreSQL:
- Parse defaults for strings and booleans properly.
- Parse the "serial" definition type properly.
- Get information on the "enum" definition type.
- Re-work getting information about keys/indices.
On MariaDB:
- Get information about lengths in indices.
- Get foreign key information separately from the rest as they can have
colliding names.
This way UNKNOWN (NULL) explicitly turns to FALSE when three-valued logic is
reduced to binary.
In pgsqlschema, however, use "IS FALSE" as boolean attributes in pg_index are
non-nullable, there is no outer join and there's no clear preference for NULL
reduction.
Over-complicated constructions in TagCloud queries have been simplified, which
should not affect their performance.
Additionally, in TagCloud's lib/subscriptionspeopleselftagcloudsection.php
a typing mistake in an equi-join of "profile_tag" and "profile_list" on
"tagger" was fixed.
That regression was introduced in f446db8e2a
Avoid the use of deprecated MariaDB "zero dates" globally. If they're present
as attribute defaults somewhere, they will be replaced with NULL implicitly.
The existing "zero dates" in MariaDB storage will be left intact and this
should not present any issues.
The "timestamp" type in table definitions now corresponds to DATETIME in
MariaDB with "DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP", which
should be close enough to the original behaviour for compatibility purposes.
It is now the recommended type for "modified" attributes, because of the
update trigger on MariaDB. But there is no such trigger implemented on
PostgreSQL as of this moment.
The code used to operate under the assumption that MariaDB doesn't support
quoting identifiers. Not only is that not exactly true, but MariaDB has
reserved keywords that cannot be used as table or column names unquoted.
