findepi commented on code in PR #12978:
URL: https://github.com/apache/datafusion/pull/12978#discussion_r1816598973
##########
datafusion/core/src/physical_optimizer/pruning.rs:
##########
@@ -1610,6 +1624,79 @@ fn build_statistics_expr(
Ok(statistics_expr)
}
+fn build_like_match(
+ expr_builder: &mut PruningExpressionBuilder,
+) -> Result<Arc<dyn PhysicalExpr>> {
+ // column LIKE literal => (min, max) LIKE literal split at % => min <=
split literal && split literal <= max
+ // column LIKE 'foo%' => min <= 'foo' && 'foo' <= max
+ // column LIKE '%foo' => min <= '' && '' <= max => true
+ // column LIKE '%foo%' => min <= '' && '' <= max => true
+ // column LIKE 'foo' => min <= 'foo' && 'foo' <= max
+
+ fn unpack_string(s: &ScalarValue) -> Result<&String> {
+ match s {
+ ScalarValue::Utf8(Some(s)) => Ok(s),
+ ScalarValue::LargeUtf8(Some(s)) => Ok(s),
+ ScalarValue::Utf8View(Some(s)) => Ok(s),
+ ScalarValue::Dictionary(_, value) => unpack_string(value),
+ _ => plan_err!("LIKE expression must be a string literal"),
+ }
+ }
+
+ fn extract_string_literal(expr: &Arc<dyn PhysicalExpr>) -> Result<&String>
{
+ if let Some(lit) = expr.as_any().downcast_ref::<phys_expr::Literal>() {
+ let s = unpack_string(lit.value())?;
+ return Ok(s);
+ }
+ plan_err!("LIKE expression must be a string literal")
+ }
+
+ // I *think* that ILIKE could be handled by making the min lowercase and
max uppercase
+ // but that requires building the physical expressions that call lower()
and upper()
+ let min_column_expr = expr_builder.min_column_expr()?;
+ let max_column_expr = expr_builder.max_column_expr()?;
+ let scalar_expr = expr_builder.scalar_expr();
+ // check that the scalar is a string literal
+ let s = extract_string_literal(scalar_expr)?;
+ // **IMPORTANT** we need to make sure that the min and max are in the
range of the prefix
+ // If we truncate 'A%' to 'A', we need to make sure that 'A' is less than
'AB' so that
+ // when we make this a range query we get 'AB' <= 'A\u{10ffff}' AND 'A' <=
'AB'.
+ // Otherwise 'AB' <= 'A' AND 'A' <= 'AB' would be *wrong* because 'AB'
LIKE 'A%' is should be true!
+ // Credit to https://stackoverflow.com/a/35881551 for inspiration on this
approach.
+ // ANSI SQL specifies two wildcards: % and _. % matches zero or more
characters, _ matches exactly one character.
+ let first_wildcard_index = s.find(['%', '_']);
+ let (min_lit, max_lit) = if let Some(wildcard_index) =
first_wildcard_index {
+ let prefix = &s[..wildcard_index];
+ let prefix_min_lit =
Arc::new(phys_expr::Literal::new(ScalarValue::Utf8(Some(
+ format!("{prefix}\u{10ffff}"),
Review Comment:
> > ... of the min value
>
> min value of what?
i get it now
So for a column we have stats: min value and max value. Let's call them
`col_min` and `col_max`.
For like `AB%` we derive lower and upper bound (`AB` and `AB\u10ffff` which
is actually incorrect, will comment about this elsewhere).
For pruning we need to check whether `[col_min, col_max] ∩ [lower_bound,
upper_bound)` is non-empty (note the upper_bound will be non-inclusive)
It's empty when `upper_bound <= col_min OR col_max < lower_bound`
It's non-empty when `upper_bound > col_min AND col_max >= lower_bound`
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