Year alias in select statement

[Peter Borissow]

Dear H2 Community,

    I ran into an unexpected error today migrating from 1.x to 2.x. I'm using H2 2.2.224 in PostgreSQL mode using the following parameters

properties.setProperty("MODE", "PostgreSQL");
properties.setProperty("DATABASE_TO_LOWER", "TRUE");
properties.setProperty("DEFAULT_NULL_ORDERING", "HIGH");

The following query is failing:

select year(date) as year from transaction

Error:

SELECT year(date) AS [*]year FROM transaction"; expected "identifier"

Looks like it doesn't like the year alias in the select statement. The following query works:

select year(date) as y from transaction

I tried the following but it didn't seem to help:

properties.setProperty("NON_KEYWORDS", "YEAR");

Any suggestions?

Thanks,

Peter

[Andreas Reichel]

Good Morning.

`YEAR` is a SQL:2016 reserved keyword: http://www.h2database.com/html/advanced.html?highlight=keyword&search=keyword#keywords

You will need to quote your alias:

SELECT Year( date ) AS "YEAR"
FROM "transaction"
;

Similar thing for `TRANSACTION`.

It is always advisable to avoid such keywords are object identifiers.

Cheers

Andreas

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[Peter Borissow]

Hi Andreas,

   Thanks for the quick reply! As you suggest, quoting "year" as the alias works. Quoting transaction didn't have any effect. Several questions:

(1) What doesn't this work?

properties.setProperty("NON_KEYWORDS", "YEAR");

(2) I am in PostgreSQL mode. On a PostgreSQL server, I don't have to quote year as an alias in PostgreSQL in a statement like this:

select date as year from transaction

Why do I have to quote year? Why has the behavior changed from 1.x to 2.x?

Thanks in advance!

Peter

To view this discussion on the web visit https://groups.google.com/d/msgid/h2-database/83c98a852da9a0ef3683051984c612304744c66c.camel%40manticore-projects.com.

[Andreas Reichel]

Greetings!

On Sat, 2024-02-17 at 00:47 +0000, 'Peter Borissow' via H2 Database wrote:

Hi Andreas,

   Thanks for the quick reply! As you suggest, quoting "year" as the alias works. Quoting transaction didn't have any effect. Several questions:

(1) What doesn't this work?

properties.setProperty("NON_KEYWORDS", "YEAR");

Because it really is just a "work around" for uncommon keywords related to more exotic features.

The problem is that the parser based on the Grammar needs to be able to distinguish the tokens. Example:

-- value can work

SELECT Year( date ) value FROM ...

vs.

-- value can work

INSERT INTO  table_name VALUE ..

Further illustration (unrelated to H2 though): https://manticore-projects.com/JSQLParser/contribution.html#manage-reserved-keywords

In short, `YEAR` seems to be a keyword that can not be worked around (for good).

(2) I am in PostgreSQL mode. On a PostgreSQL server, I don't have to quote year as an alias in PostgreSQL in a statement like this:

select date as year from transaction

The Compatibility modes are "certain syntax and functions are emulated" modes. The Developers don't aim or claim full compliance.

Example: NEXT VALUE for a sequence is supported for all 3 syntax (Postgres, Oracle and MS SQL Server) as a courtesy (which I find just awesome). But non of those dialect is fully implemented (and will never be).

Why do I have to quote year? Why has the behavior changed from 1.x to 2.x?

Because H2 has massively evolved since and supports now a more complex Grammar.

More Grammar, more restricted keywords.

Example: When you don't support `Exclusive` lock modes, then `Exclusive` is not needed as a keyword. But when support is added, then suddenly `Exclusive` becomes a keyword.

Thus it is best practise to avoid all SQL:2016 reserved keywords (long list!) and/or to quote identifiers always.

(If you have a massive library of existing statements, then you could engage JSQLParser and a) identify all such colliding identifiers and/or b) rewrite your statements quoting the identifiers.)

Good luck

Andreas

[Andreas Reichel]

On Sat, 2024-02-17 at 08:09 +0700, Andreas Reichel wrote:

Quoting transaction didn't have any effect.

Try again on MS SQL Server 😄

[Peter Borissow]

Thank you. I get it. Compatibility mode with PostgreSQL is incomplete and certain regressions are to be expected when jumping major versions.

I would be willing to help patch the sw. Whether I would succeed is another matter :-)

I'll pull the source and start a new thread as needed.

Many thanks to you and the team. Love H2!

Best,

Peter

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[Andreas Reichel]

Please discuss with the H2 developers first.

My understanding is: the current trend goes to SQL:2016 compliance and the Compatibility modes are more or less seen as a tolerated legacy. So any extension of those modes may not be welcome unconditionally, when it introduced complexity or maintenance issues. I may be wrong of course.

Cheers

Andreas

[Evgenij Ryazanov]

Hello!

YEAR is a reserved word even in archaic SQL-92, so it was a bad idea to use it as unquoted identifier. BTW, DATE and TRANSACTION are reserved words too, but H2 allows their usage as identifiers. Also there is no YEAR function in the Standard, correct syntax is EXTRACT(YEAR FROM someValue).

Newer versions of H2 may have more keywords than old versions and reserved words from the latest version of the SQL Standard (from SQL:2023 for now) are potential candidates.
 
Anyway, the following test case prints 2024 as expected, so NON_KEYWORDS settings works well and you have some other problem in your application, most likely your query is executed from a connection with different settings.

Properties p = new Properties();

p.put("MODE", "PostgreSQL");

p.put("DATABASE_TO_LOWER", "TRUE");

p.put("DEFAULT_NULL_ORDERING", "HIGH");

p.put("NON_KEYWORDS", "YEAR");

try (Connection connection = DriverManager.getConnection("jdbc:h2:mem:", p)) {

Statement s = connection.createStatement();

s.execute("CREATE TABLE transaction(date DATE) AS VALUES CURRENT_DATE");

ResultSet rs = s.executeQuery("SELECT year(date) AS year FROM transaction");

rs.next();

System.out.println(rs.getInt(1));

}

[Peter Borissow]

Thanks for checking Evgenij. I was mistaken - adding "YEAR" to the "NON_KEYWORDS" does indeed work. There was a different issue on my end that was throwing things off. Appreciate everyone's help.

Best,

Peter

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