'array_repeat' if the repeat count value is 0, return NULL instead of empty array

[jatin510]

Which issue does this PR close?

Closes #13872.

Rationale for this change

We noticed that,
Array of null: []
Empty array: []

> select array_repeat(null, 0);
+-----------------------------+
| array_repeat(NULL,Int64(0)) |
+-----------------------------+
| []                          |
+-----------------------------+
1 row(s) fetched. 
Elapsed 0.006 seconds.

> select array_repeat(null, 1);
+-----------------------------+
| array_repeat(NULL,Int64(1)) |
+-----------------------------+
| []                          |
+-----------------------------+

Appears same

To distinguish both,
Updated the empty array to return null instead
Array of null: []
Empty array will return: null
Now,

> select array_repeat(null, 0);
+-----------------------------+
| array_repeat(NULL,Int64(0)) |
+-----------------------------+
|                             |
+-----------------------------+
1 row(s) fetched. 
Elapsed 0.025 seconds.

> select array_repeat(null, 1);
+-----------------------------+
| array_repeat(NULL,Int64(1)) |
+-----------------------------+
| []                          |
+-----------------------------+

What changes are included in this PR?

Are these changes tested?

Yes,

Updated the array.slt file

Are there any user-facing changes?

Yes

It has breaking change. Please add the label api change

[jonahgao]

I think we should fix it on the display/formatting side. For example, we still cannot distinguish:

DataFusion CLI v44.0.0

> select array[], array[null];
+--------------+------------------+
| make_array() | make_array(NULL) |
+--------------+------------------+
| []           | []               |
+--------------+------------------+
1 row(s) fetched.
Elapsed 0.007 seconds.

See #13872 (comment)

[jatin510]

I think we should fix it on the display/formatting side. For example, we still cannot distinguish:

DataFusion CLI v44.0.0

> select array[], array[null];
+--------------+------------------+
| make_array() | make_array(NULL) |
+--------------+------------------+
| []           | []               |
+--------------+------------------+
1 row(s) fetched.
Elapsed 0.007 seconds.

See #13872 (comment)

makes sense,
should we start showing NULL for the null values ?
It will make things easy for us. Even the postgres, apache spark and others shows, NULL for null values.

> select array[], array[null];
+--------------+------------------+
| make_array() | make_array(NULL) |
+--------------+------------------+
| []           | [NULL]           |
+--------------+------------------+
1 row(s) fetched.
Elapsed 0.007 seconds.

This will make changes everywhere.
I think we should start showing NULL for null values.

@jayzhan211 @jonahgao

[jayzhan211]

I think we should fix it on the display/formatting side. For example, we still cannot distinguish:

DataFusion CLI v44.0.0

> select array[], array[null];
+--------------+------------------+
| make_array() | make_array(NULL) |
+--------------+------------------+
| []           | []               |
+--------------+------------------+
1 row(s) fetched.
Elapsed 0.007 seconds.

See #13872 (comment)

makes sense, should we start showing NULL for the null values ? It will make things easy for us. Even the postgres, apache spark and others shows, NULL for null values.

> select array[], array[null];
+--------------+------------------+
| make_array() | make_array(NULL) |
+--------------+------------------+
| []           | [NULL]           |
+--------------+------------------+
1 row(s) fetched.
Elapsed 0.007 seconds.

This will make changes everywhere. I think we should start showing NULL for null values.

@jayzhan211 @jonahgao

Display nulls looks fine to me

[jatin510]

Why haven’t we been displaying null values as NULL so far?
What was the original reasoning or intention behind this decision?

[jonahgao]

Why haven’t we been displaying null values as NULL so far? What was the original reasoning or intention behind this decision?

I guess it's to follow PostgreSQL CLI. PostgreSQL CLI does not display null values as well, but it always displays null elements of arrays as NULL.

$ psql
psql (16.6 (Ubuntu 16.6-0ubuntu0.24.04.1))
Type "help" for help.

psql=> select null, array[null, 1, null];
 ?column? |     array
----------+---------------
          | {NULL,1,NULL}
(1 row)

psql=> \pset null mynull
Null display is "mynull".
psql=> select null, array[null, 1, null];
 ?column? |     array
----------+---------------
 mynull   | {NULL,1,NULL}
(1 row)

I think we can follow PostgreSQL more thoroughly, or always display null, regardless of whether it is a list element.
The latter can be achieved by setting FormatOptions.

The fix should not involve the DataFusion core; it should be related to DataFusion CLI and sqllogictests.
Some displays of DataFusion CLI are not user-friendly, for example

DataFusion CLI v44.0.0

> select array[null, null, null,1,null];
+------------------------------------------+
| make_array(NULL,NULL,NULL,Int64(1),NULL) |
+------------------------------------------+
| [, , , 1, ]                              |
+------------------------------------------+
1 row(s) fetched.
Elapsed 0.006 seconds.

[jatin510]

Created a different PR as this is related to specific array udf.
Introducing default cli formatter for sqllogic test and df-cli : #14052

Thanks, @jonahgao @jayzhan211 for your valuable feedback.