Add postgreSql character length functions

[griffio]

Add postgreSql character length functions
Add fixture test for use with constraint checks
Add integration test for use with client

Returns number of characters in the string or will return NULL if expression is NULL.

PostgreSQL supports Ansi CHAR_LENGTH, CHARACTER_LENGTH.
It also supports LENGTH, which is a PostgreSQL alias for CHAR_LENGTH.

• length ( In MySql the length function is in bytes )
• char_length
• character_length

Multibyte characters count as a single character, not as bytes.

Examples

char_length ( text ) -> integer
char_length( 'jose' ) -> 4
char_length( '海豚' ) -> 2
char_length( NULL ) -> NULL

TODO

Add to MySql

❓ One question for the reviewer -- how to make the PostgreSqlTypeResolver.kt so that the char functions will type check string expressions and fail if passed a numeric?
e.g error function character_length(integer) does not exist

[hfhbd]

AFAIK there is no sql type checker. While the compiler is able to get the expected Kotlin type, eg for SELECT length(?) to specify the Kotlin parameter (here String), there is no check, if the actual SQL function could handle this SQL type, like: SELECT length(42). And I don't think, there will be a SQL type checker in the future.

[hfhbd]

Thanks!
Let's add MySql (and other dialects) in another PR.

[griffio]

Ok. To try and understand further - using a bind variable - would it be expected for the SqlFunctionExpr to generate code to express e.g string->int ?

Would this work if the bind parameter is not related to a SqlColumn?

Given

selectLength:
  SELECT length(?);

val length = queries.selectLength("abc").executeAsOne()

results in mismatch: inferred type is String but Long? was expected

Maybe this is not supported

[hfhbd]

Yes, this should work! Could you add it as a test? I I will take a look later.

Found bug

[griffio]

@hfhbd Thanks - Added failing test here 04ad12f

This problem already existed with calling functions

Type mismatch: inferred type is String but Int? was expected

Maybe it's related to this https://github.com/cashapp/sqldelight/pull/3431/files
Can only infer the same type? 🤔

[hfhbd]

Thanks.
I think, there is a bigger root cause: we currently don't really have a good representation of a function, including the typed parameters. At the moment, we only specify the return type. The added Kotlin parameter type inference needs other typed sql parameters. In the past, to specify the kotlin type, you need to use a CAST. Ideally, we need a better function representation to specify the type of the parameters.

[hfhbd]

I was just about to ask to revert the test.
I am fine with merging this.

Rewriting the function implementation is another issue and properly won't make it into 2.0.