fix(query): fix shrink_d256 for negative value (#15574)

Author: sundy-li

src/query/expression/src/utils/mod.rs

@@ -174,10 +174,16 @@ fn shrink_d256(decimal: i256, size: DecimalSize) -> Scalar {
     let valid_bits = 256 - decimal.saturating_abs().leading_zeros();
     let log10_2 = std::f64::consts::LOG10_2;
     let mut precision = ((valid_bits as f64) * log10_2).floor() as u8;
-    if decimal >= i256::from(10).pow(precision as u32) {
+
+    if decimal.saturating_abs() >= i256::from(10).pow(precision as u32) {
         precision += 1;
     }
-    precision = precision.clamp(1, MAX_DECIMAL256_PRECISION).max(size.scale);
+
+    // adjust precision to the maximum scale of the decimal type
+    if precision < size.scale {
+        precision = size.scale;
+    }
+    precision = precision.clamp(1, MAX_DECIMAL256_PRECISION);
 
     let size = DecimalSize { precision, ..size };
     let decimal_ty = DecimalDataType::from_size(size).unwrap();

tests/sqllogictests/suites/base/11_data_type/11_0006_data_type_decimal.test

@@ -262,6 +262,7 @@ SELECT CAST(987654321.34 AS DECIMAL(76, 2)) / CAST(1.23 AS DECIMAL(76, 2)) AS re
 ----
 802970992.95934959
 
+
 ## negative
 
 query I
@@ -371,6 +372,17 @@ DECIMAL(41, 3) DECIMAL(41, 3) DECIMAL(76, 5) DECIMAL(48, 8)
 
 ## compare
 
+## issue: https://github.com/datafuselabs/databend/issues/15568
+query IIII
+SELECT (0.123)>(-1.1), (0.1234)>(-1.1), (0.1234)>(-12.1), (0.1234)>(-123.1)
+----
+1 1 1 1
+
+query IIII
+SELECT (0.12)>(1.1), (0.1)>(-1.1), (0.12)>(-1.12), (0.12)>(-1);
+----
+0 1 1 1
+
 query IIIII
 select a > b, a < b, a = b, a != b, a <= b, a >= b from (select 3::Decimal(13,2) a , 3.1::Decimal(8,2) b);
 ----