support: no param function: localtime

[AbhishekASLK]

This PR enriches the AST by adding proper support for parsing LOCALTIME as a dedicated expression node instead of treating it as a column.

SQL:

from sqlglot import parse_one

query = """
SELECT LOCALTIME;
"""

expression = parse_one(query)
print(repr(expression))

Previously:

Select(
  expressions=[
    Column(
      this=Identifier(this=LOCALTIME, quoted=False))])

Now:

Select(
  expressions=[
    LocalTime()])

[georgesittas]

What dialect supports LOCALTIME as a no-parentheses function?

[AbhishekASLK]

What dialect supports LOCALTIME as a no-parentheses function?

• MySQL
• Snowflake
• Postgres
• Flink
• Trino

we need to test for all the dialect present in sqlglot? as i only tested for 11 and from that i found these support it.

[georgesittas]

we need to test for all the dialect present in sqlglot? as i only tested for 11 and from that i found these support it.

We generally want to test the most common dialects, i.e.:

# yes: supports localtime, no: does not support it
Athena - yes
BigQuery - no
ClickHouse - no
Spark - no
DuckDB - yes
Oracle - no
Presto - yes
Redshift - no
Snowflake - yes
Trino - yes
mssql - no

[georgesittas]

Please add tests for this PR:

• For the dialects that don't support LOCALTIME, we should test that SELECT localtime roundtrips without being changed & that selects[0].assert_is(exp.Column)
• For the dialects that support it, LOCALTIME should roundtrip to the supported syntax. You may need to add logic in the generator for rewriting it to LOCALTIME instead of LOCALTIME() which is the default.

[georgesittas]

The Func subclass names have implicit semantics. If you do LocalTime, that means the parser will recognize and produce this expression for LOCAL_TIME, not LOCALTIME.

Suggested change

	class LocalTime(Func):
	class Localtime(Func):

[georgesittas]

We should pop this token off of KEYWORDS for BigQuery, ClickHouse, Hive (affects Spark2, Spark, Databricks– which is correct), Oracle, Redshift, T-SQL. Otherwise, we'll incorrectly produce a Localtime node instead of a Column. See this comment.