Support UPPER & LOWER non-aggregating functions

Remove StoreError, now fetch_schema returns Result<Option<Schema>>.
StoreError::SchemaNotFound was error, but now it simply returns "None".

Change Store->fetch_schema interface return type to Option<_>,

[Revised] Support Plus(+) and Minus(-) signs in WHERE

Convert generate_id, insert_data and delete_data to async.
Now all StoreMut functions provide async

Getting familiar with using TryStreamExt

…rror

…N test cases!

Replace or-iterator to or-stream.
Update BlendContext retun type to Option rather than Result.

FilterContext can have both content & children or only children.

Convert store traits to async

Update Store traits not to require std::marker::Send

INSERT INTO TestA (id, num, name) SELECT id, num, name FROM Test
Above SQL INSERT query using SELECT is now supported.

pr:  #123 

Added benchmarks to constantly check the performance increase / regression while programming.
Added 'select_many', 'select_one_tainted', 'select_many_tainted'

fix: Changed parse.rs to parse_sql.rs

Add err_into function to handle "impl Error" -> StorageError -> gluesql::Error conversion.

In sled_storage/,
Detach error codes from mod.rs and move to error.rs.
Detach impl StoreMut from store.rs and move to store_mut.rs.

Clean up sled_storage implementation codes

Replace Rc<Vec<_>> to Rc<[_]>, make codes clippy clean

Update StoreMut insert_data interface to get multiple rows,
- StoreMut->insert_data now takes Vec<Row>.
- Remove StoreMut->generate_id, it was only for insert_data.
- Add StoreMut->update_data to handle UPDATE sql query.

Update StoreMut delete_data param from &T to Vec<T>

Apply sled transaction to StoreMut insert_data, update_data and delete_data.

Sorry for the second pull, but this should cover the rest.

Allow Binary Operations Between <i64> and <f64>

Implements UNIQUE constraint in CREATE TABLE.
Supports multiple NULL values for Unique constraint.

Add mdbook based documentation 🎉

Add data type validation to `validate_rows`.
Now inserting & updating values which does not fit to column's data type is not allowed.

Single quoted string is now supported in INSERT.
INSERT INTO Foo VALUES ("hello", 'world');

Implement CAST([value] AS [type])
e.g. CAST (10 AS TEXT)

Migrate to the latest version of sqlparser crate.
Add JOIN without constraint query support.
e.g. SELECT * FROM Item JOIN Player

… /book

Add Value::TryFromLiteral to replace cast_ast_value in evaluated.rs.
Now it can handle CAST(1 AS FLOAT).
Test cases in function::cast::cast_literal reach all branches in Value::TryFromLiteral match.

Provide OptBool, OptI64, OptF64 and OptStr CAST supports.
Add unit tests to CAST on Value.

No more OptBool, OptI64, OptF64, OptStr and Empty, all converges into Value::Null

Value::Null != Value::Null, and it should also work same with AstValue::Null.
Fix to Value::Null != AstValue::Null and also fixes nullable test cases.

Now Null != Null so the name GroupKey::Null does not sound good.
None keyword in Rust implies Eq, so rename Null to None for GroupKey.

UniqueKey implements Eq & Hash but Null != Null, so Eq should not work for Null.
To make the meaning clear, replace UniqueKey::Null to Option<UniqueKey>.

Replace Value::Opt- & Empty to Value::Null!

Two keywords AstValue and literal were used together, but now unify to only use Literal

There were some reachable errors in evaluate.rs but marked as Unreachable-.
Remove some fake unreachable errors, and replace to reachable named errors.

Replace to Evaluated::Literal by cloning string value

No more ValueRef, Cow can take both Value & ValueRef

Now Evaluated enum only has Literal and Value.

Apply Cow to Evaluate, remove -Ref types

Now Literal means crate::data::Literal, no more sqlparser::ast::Value.

… (#181)

Remove redundant type validation in INSERT & UPDATE which are covered by Row::new and Update::apply.

Fill missing validation branches from INSERT & UPDATE.
- INSERT & UPDATE using literals
- INSERT & UPDATE using nested select
- checking null for all cases

Fix type validation to check all possible branches from INSERT & UPDATE

… COLUMN