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fix: substr - correct behaivour with negative start pos #1660

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merged 1 commit into from
Jan 31, 2022
Merged

fix: substr - correct behaivour with negative start pos #1660

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67 changes: 67 additions & 0 deletions datafusion/src/physical_plan/functions.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3582,6 +3582,18 @@ mod tests {
StringArray
);
#[cfg(feature = "unicode_expressions")]
test_function!(
Substr,
&[
lit(ScalarValue::Utf8(Some("joséésoj".to_string()))),
lit(ScalarValue::Int64(Some(-5))),
],
Ok(Some("joséésoj")),
&str,
Utf8,
StringArray
);
#[cfg(feature = "unicode_expressions")]
test_function!(
Substr,
&[
Expand Down Expand Up @@ -3680,6 +3692,61 @@ mod tests {
StringArray
);
#[cfg(feature = "unicode_expressions")]
test_function!(
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postgres=# select a from t;
    a
----------
 alphabet
(1 rows)

postgres=# select substring(a, 0, 5) from t;
 substring
-----------
 alph
(1 rows)

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Hi @ovr, Sorry, I think there are still some problems.

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@ovr ovr Jan 24, 2022 •
edited
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You are right, i did another iteration and looks like I found a way how to get similar behaviour

PG:

select substr('alphabet', 0, 5) as s1, substr('alphabet', -5, 10) as s2, substr('alphabet', -5, 4) as s3;
| s1.    | s2     | s3   |
| :---- | :---- | :--- |
| alph  | alph |         |

DF:

❯ select substr('alphabet', 0, 5) as s1, substr('alphabet', -5, 10) as s2, substr('alphabet', -5, 4) as s3;
+------+------+----+
| s1   | s2   | s3 |
+------+------+----+
| alph | alph |    |
+------+------+----+
1 row in set. Query took 0.016 seconds.

Thanks

Substr,
&[
lit(ScalarValue::Utf8(Some("alphabet".to_string()))),
lit(ScalarValue::Int64(Some(0))),
lit(ScalarValue::Int64(Some(5))),
],
Ok(Some("alph")),
&str,
Utf8,
StringArray
);
// starting from 5 (10 + -5)
#[cfg(feature = "unicode_expressions")]
test_function!(
Substr,
&[
lit(ScalarValue::Utf8(Some("alphabet".to_string()))),
lit(ScalarValue::Int64(Some(-5))),
lit(ScalarValue::Int64(Some(10))),
],
Ok(Some("alph")),
&str,
Utf8,
StringArray
);
// starting from -1 (4 + -5)
#[cfg(feature = "unicode_expressions")]
test_function!(
Substr,
&[
lit(ScalarValue::Utf8(Some("alphabet".to_string()))),
lit(ScalarValue::Int64(Some(-5))),
lit(ScalarValue::Int64(Some(4))),
],
Ok(Some("")),
&str,
Utf8,
StringArray
);
// starting from 0 (5 + -5)
#[cfg(feature = "unicode_expressions")]
test_function!(
Substr,
&[
lit(ScalarValue::Utf8(Some("alphabet".to_string()))),
lit(ScalarValue::Int64(Some(-5))),
lit(ScalarValue::Int64(Some(5))),
],
Ok(Some("")),
&str,
Utf8,
StringArray
);
#[cfg(feature = "unicode_expressions")]
test_function!(
Substr,
&[
Expand Down
28 changes: 18 additions & 10 deletions datafusion/src/physical_plan/unicode_expressions.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -457,21 +457,29 @@ pub fn substr<T: StringOffsetSizeTrait>(args: &[ArrayRef]) -> Result<ArrayRef> {
start,
count
)))
} else if start <= 0 {
Ok(Some(string.to_string()))
} else {
let graphemes = string.graphemes(true).collect::<Vec<&str>>();
let start_pos = start as usize - 1;
let count_usize = count as usize;
if graphemes.len() < start_pos {
let (start_pos, end_pos) = if start <= 0 {
let end_pos = start + count - 1;
(
0_usize,
if end_pos < 0 {
// we use 0 as workaround for usize to return empty string
0
} else {
end_pos as usize
},
Comment on lines +466 to +471
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Suggested change
if end_pos < 0 {
// we use 0 as workaround for usize to return empty string
0
} else {
end_pos as usize
},
0_usize.max(end_pos as usize),

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@ovr would you like to make this change so we can merge the PR? I can find some time to do so too if that would help.

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@jimexist It doesn't work because it doesn't reflect comparing with less than 0. -1 (i32) with as usize will produce a maximum number that can be stored in usize.

image

@alamb It doesnt work.

)
} else {
((start - 1) as usize, (start + count - 1) as usize)
};

if end_pos == 0 || graphemes.len() < start_pos {
Ok(Some("".to_string()))
} else if graphemes.len() < start_pos + count_usize {
} else if graphemes.len() < end_pos {
Ok(Some(graphemes[start_pos..].concat()))
} else {
Ok(Some(
graphemes[start_pos..start_pos + count_usize]
.concat(),
))
Ok(Some(graphemes[start_pos..end_pos].concat()))
}
}
}
Expand Down