This patch introduces the ability execute parsed SQL statements. The
abstract AST Statement node now has a virtual 'execute' method. This
method takes a Database object as parameter and returns a SQLResult
object.
Also introduced here is the CREATE SCHEMA statement. Tables live in a
schema, and if no schema is present in a table reference the 'default'
schema is implied. This schema is created if it doesn't yet exist when
a Database object is created.
Finally, as a proof of concept, the CREATE SCHEMA and CREATE TABLE
statements received an 'execute' implementation. The CREATE TABLE
method is not able to create tables created from SQL queries yet.
The Order enum is used in the Meta component of LibSQL. Using this enum
meant having to include the monster AST/AST.h include file. Furthermore,
they are sort of basic and therefore can live in the general SQL
namespace. Moved to LibSQL/Type.h.
Also introduced a new class, SQLResult, which is needed in future
patches.
SQL was standardized before there was consensus on sane language syntax
constructs had evolved. The language is mostly case-insensitive, with
unquoted text converted to upper case. Identifiers can include lower
case characters and other 'special' characters by enclosing the
identifier with double quotes. A double quote is escaped by doubling it.
Likewise, a single quote in a literal string is escaped by doubling it.
All this means that the strategy used in the lexer, where a token's
value is a StringView 'window' on the source string, does not work,
because the value needs to be massaged before being handed to the
parser. Therefore a token now has a String containing its value. Given
the limited lifetime of a token, this is acceptable overhead.
Not doing this means that for example quote removal and double quote
escaping would need to be done in the parser or in AST node
construction, which would spread lexing basically all over the place.
Which would be suboptimal.
There was some impact on the sql utility and SyntaxHighlighter component
which was addressed by storing the token's end position together with
the start position in order to properly highlight it.
Finally, reviewing the tests for parsing numeric literals revealed an
inconsistency in which tokens we accept or reject: `1a` is accepted but
`1e` is rejected. Related to this is the fate of `0x`. Added a FIXME
reminding us to address this.
