SQLite Forum

SQL compliance on Wikipedia
Yes, but interoperability ≠ compliance with a proprietary standard that cost $2000 USD to purchase and read.

I work at making SQLite interoperable with PostgreSQL (mostly) but also
MySQL and SQL Server.  Witness the fact that SQLite mimics some of the
quirks of those other systems, such as MySQL back-tics
(ex: <tt>\`name\`</tt>) and SQL Server's use of square brackets
(ex: <tt>[name]</tt>).  For RCEs, differing systems have different
requirements for the use or non-use of the RECURSIVE keyword.  SQLite
works the same regardless, so that it can interoperate with everybody.
Different systems place different restrictions on the position and
content of computed columns.  SQLite has no restrictions at all, so
that it interoperates with everyone.  Other engines are very particular
about the datatype names they will accept.  SQLite accepts any datatype
name you want, so that it interoperates with everybody.  And so forth.

If you have specific suggestions on how SQLite could interoperate better
with other common systems, that would be great.

The previous paragraphs demonstrate that interoperability does not
imply standard compliance.  Note further that
standards compliance does not imply interoperability.  The
brief glimpses I have had of the SQL standards leave lots of details either
ambiguous, or implementation defined.  It is not difficult to find
two standards-compliant SQL database engines that will not interoperate.