What is the significance of literal("a") vs "b" in concat example?

[anentropic]

https://docs.sqlalchemy.org/en/20/core/functions.html#sqlalchemy.sql.functions.concat

String concatenation in SQLAlchemy is more commonly available using the Python + operator with string datatypes, which will render a backend-specific concatenation operator, such as :

>>> print(select(literal("a") + "b"))
SELECT :param_1 || :param_2 AS anon_1

It's unclear to me in this example if:

• wrapping "a" in literal(...) is optional (as demonstrated by "b" doesn't have it)
• the first concat item has to be wrapped in literal(...), perhaps for operator overloading reasons, but it's optional for subsequent items
• only the first item must be wrapped in literal(...) and subsequent items must not have it
• there's something contextual about why literal("a") but not literal("b") that I am not getting

[anentropic]

or... I guess "b" is an SQL column name, as python string, while literal("a") is the SQL string "a"

[anentropic]

or... I guess "b" is an SQL column name, as python string, while literal("a") is the SQL string "a"

🤔 that idea made sense, but in fact they both seem to be treated as SQL string literals

select(
    literal("local-") + "gamesession.id",
    ...
)

gives [('local-gamesession.id', ...)]

and

select(
    literal("local-") + GameSession.id,
    ...
)

gives [(3, ...)] so the literal gets lost in this case

select(
    text("'local-' || gamesession.id"),
    ...
)

works, but it's just raw SQL and not using SQLAlchemy concat feature

[CaselIT]

Hi,

literal is generated automatically when using a literal with any sqlalchemy construct. So column('foo') + 1 is equivalent to column('foo') + literal(1)

In the example literal is explicit because otherwise the operation would be done by python: select('a' + 'b') is the same as select('ab'), meaning that it will generate SELECT :param_1 AS anon_1