As @vforchi said:

> The ANSI standard `||` is supported only by Oracle and Postgres: MySQL uses
> `CONCAT` and SQLServer uses `+`.

_This commit resolves the issue #70 ._

* The parsing did not allow unsigned numerics and SQL SET functions as
  specified in the ADQL 2.0 grammar

* It was even forbidden to put a column whose the type is not String.

* The translation of a concatenation expression was always prefixed by the
  ADQLList's name: CONCAT_STR. Of course, no database likes that...

Regarding this last point, this commit fixes the GitHub issue #54

if the alias is not delimited in ADQL.

This commit fixes the GitHub issue #56

are translated: the table part (if a reference to an aliased table) should be
as declared in the DBTable (especially now that we have DBTableAlias to deal
nicely with table aliases).

this table is declared with an alias. Instead, the table alias must be used.

Note: This problem occurred only when ADQLParser was used with a DBChecker.

This commit fixes the GitHub issue #53

and HashMap more generic by returning resp. a List and Map instead.

In the resulting SQL query, if there are an alias on the joined tables, these
aliases must be used in the ON clause (instead of the full table name).

For instance, the following ADQL query:

```sql
  SELECT *
  FROM tableA AS a NATURAL JOIN tableB AS b;
```

should be translated into the following SQL:

```sql
  SELECT *
  FROM tableA AS a
    INNER JOIN tableB AS b
      ON a.id = b.id
```

This commit complete the resolution of the Pull Request #16
(more details about the issue can be got in there)

In MS-SQLServer, the following functions return a value of the same
type as the given argument:
  - abs
  - ceiling
  - degrees
  - floor
  - radians
  - round.

Since ADQL requires that these functions return a DOUBLE
(i.e. a float in MS-SQLServer), it must be ensured that the given
argument is a float.

This commit partially fixes the Pull Request #16

On the contrary to other DBMS, MySQL supports schemas, but as databases.
Which means that JDBCConnection gets from the JDBC driver that MySQL does
not support schemas and so it tries to access TAP_SCHEMA tables with a
'TAP_SCHEMA_' prefix instead of 'TAP_SCHEMA.' one. Since MySQL does
behave like it supports schemas, JDBCConnection.supportsSchema must be
set to 'true' if the DBMS is MySQL.

Besides, since no schemas are returned by the JDBC driver
(cf DatabaseMetadata.listSchema(...)), the function
JDBCConnection.isSchemaExisting(String, DatabaseMetaData) must always assume
that the specified schema exists if the DBMS is MySQL. This is particularly
important when the existence of 'TAP_UPLOAD' must be checked, because if the
function returns 'false' the library will attempt to create the database/schema
'TAP_UPLOAD' and will obviously fail due to a lack of permissions. Of course,
it means that the TAP implementor must create manually the schema/database
'TAP_UPLOAD' him-/her-self.

The second particularity of MySQL is the quote character for identifiers.
It is a back-quote (`) instead of a double quote ("). To reflect this
difference, JDBCTranslator.appendIdentifier(...) has been overwritten in a new
JDBCTranslator extension: MySQLTranslator.

The translation of all SQL types and mathematical functions have been adapted to
MySQL according to the online documentation. Few tests have been done locally
with a tiny database. This seems to work but further testing should be
performed in order to ensure the stability of this implementation.

This import can not be resolved in a standalone version of adql. It
also creates a circular dependency: ADQL then depends on TAP, which
depends on starjava, but starjava depends on ADQL.

This is particularly annoying for numeric functions like sqrt(...)
(example query: SELECT TOP 1 sqrt(2) as s2 FROM whatever_table).
This bug has been raised by M. Taylor.

These two columns let recommend an order, respectively, for tables in their
schema, and columns in their table.
In addition of these new columns, "arraysize" has been also added.
All these new columns are already supported when creating a TAP_SCHEMA from
an XML file.

[ADQL] SqlServerTranslator: bug fix for TOP vs LIMITgrammar. Adding support for math functions, including translations for TRUNCATE and MOD non-standard implementation.

This function was originally static. Since no other classes benefits of this
static state, this function is no longer static. This might however raise a
small incompatibility for the users of the library which used it.

deals with NATURAL JOINs and JOINs using the keyword USING so that being
supported by SQL Server. Basically, they are translated as a list of ON
conditions.
Warning: This translator is just guaranteed to solve the NATURAL and USING
issue. Support for datatypes conversion and case sensitivity has to be
reviewed. Besides no geometrical function is translated for SQL Server.

functions must be casted into NUMERIC. Otherwise Postgres rejects the query.

Now, all occurences of ' are replaced by '' in the SQL translation.

(merge with branch 'unknownFctType')

[ADQL] Rename UnresolvedJoin and UnresolvedFunction so that normalizing all UnresolvedXxx exceptions.

[TAP] Add an XML TableSet parser. The main modification done in JDBCConnection is about the schema prefix of table when the DBMS does not support schemas: now, only standard tables are expected with the prefix 'TAP_SCHEMA_' and the upload tables also with 'TAP_UPLOAD_'.

[ADQL,TAP] Add geometry format in output and correct upload of STC-S regions. Geometrical type conversion from and into a DB type is now required in all JDBCTranslator. This allows formatting of geometrical column value coming from the database, but also the translation of STC-S expressions provided in uploaded table into geometrical column values.

[ADQL] Support the special escaping syntax for string literals in Postgres (strings to escape must be prefixed by a E before the starting ').

[ADQL] Fix SQL translation of NOT BETWEEN (before it was translated by just BETWEEN ; NOT was forgotten)

[ADQL] Fix SQL translation of operations' alias: now, the alias is always surrounded by double quotes (so a sum between two numbers won't have the default alias +, but it will have +)

[TAP,ADQL] Improve and remake a part of the database connection. Missing javadoc has been added when missing in the modified tables.

ADQL: Fix big bug: no parenthesis in the SQL translation for ADQL constraints with parenthesis ( ex: A AND (B OR C)) )

ADQL: Correct version number for all modified ADQL related classes since the official v1.1 release. Now, version number after any modification in ADQL is v1.2.

ADQL: Completely change/improve Joins management, and particularly NATURAL JOIN and USING JOIN. Now, every joined columns are represented by a DBCommonColumn instance which has a given table coverage.
Before, there was a problem while using at least 3 or 4 NATURAL JOINs. Bug raised by Menelaos Perdikeas (ESAC).