[fix](named_struct) fix named_struct signature which deduce wrong for nested decimal precision

fe/fe-core/src/main/java/org/apache/doris/nereids/trees/expressions/functions/scalar/CreateNamedStruct.java

@@ -21,7 +21,8 @@
 import org.apache.doris.nereids.exceptions.AnalysisException;
 import org.apache.doris.nereids.trees.expressions.Expression;
 import org.apache.doris.nereids.trees.expressions.functions.AlwaysNotNullable;
-import org.apache.doris.nereids.trees.expressions.functions.ExplicitlyCastableSignature;
+import org.apache.doris.nereids.trees.expressions.functions.ComputePrecision;
+import org.apache.doris.nereids.trees.expressions.functions.CustomSignature;
 import org.apache.doris.nereids.trees.expressions.functions.ExpressionTrait;
 import org.apache.doris.nereids.trees.expressions.literal.StringLikeLiteral;
 import org.apache.doris.nereids.trees.expressions.visitor.ExpressionVisitor;
@@ -38,12 +39,9 @@
 /**
  * ScalarFunction 'named_struct'.
  */
-public class CreateNamedStruct extends ScalarFunction
-        implements ExplicitlyCastableSignature, AlwaysNotNullable {
+public class CreateNamedStruct extends ScalarFunction implements CustomSignature, ComputePrecision, AlwaysNotNullable {
 
-    public static final List<FunctionSignature> SIGNATURES = ImmutableList.of(
-            FunctionSignature.ret(StructType.SYSTEM_DEFAULT).args()
-    );
+    public static final FunctionSignature SIGNATURE = FunctionSignature.ret(StructType.SYSTEM_DEFAULT).args();
 
     /**
      * constructor with 0 or more arguments.
@@ -83,23 +81,29 @@ public CreateNamedStruct withChildren(List<Expression> children) {
     }
 
     @Override
-    public <R, C> R accept(ExpressionVisitor<R, C> visitor, C context) {
-        return visitor.visitCreateNamedStruct(this, context);
+    public FunctionSignature computePrecision(FunctionSignature signature) {
+        return signature;
     }
 
     @Override
-    public List<FunctionSignature> getSignatures() {
+    public FunctionSignature customSignature() {
         if (arity() == 0) {
-            return SIGNATURES;
+            return SIGNATURE;
         } else {
             ImmutableList.Builder<StructField> structFields = ImmutableList.builder();
             for (int i = 0; i < arity(); i = i + 2) {
                 StringLikeLiteral nameLiteral = (StringLikeLiteral) child(i);
                 structFields.add(new StructField(nameLiteral.getStringValue(),
                         children.get(i + 1).getDataType(), true, ""));
             }
-            return ImmutableList.of(FunctionSignature.ret(new StructType(structFields.build()))
-                    .args(children.stream().map(ExpressionTrait::getDataType).toArray(DataType[]::new)));
+            return FunctionSignature.ret(new StructType(structFields.build()))
+                    .args(children.stream().map(ExpressionTrait::getDataType).toArray(DataType[]::new));
         }
     }
+
+    @Override
+    public <R, C> R accept(ExpressionVisitor<R, C> visitor, C context) {
+        return visitor.visitCreateNamedStruct(this, context);
+    }
+
 }

regression-test/data/query_p0/sql_functions/struct_functions/test_struct_functions.out

@@ -39,3 +39,10 @@ a	\N	abc
 \N	\N	\N
 NULL	null	\N
 
+-- !sql_before --
+{"col_11":123.321, "col_12":{"col":1, "col1":345.24}}
+
+-- !sql_after --
+{"col_11":123.321, "col_12":{"col":1, "col1":345.24}}
+{"col_11":123.321, "col_12":{"col":1, "col1":12345.24}}
+

regression-test/data/query_p0/sql_functions/struct_functions/test_struct_functions_by_literal.out

@@ -35,3 +35,9 @@
 -- !sql --
 10000000000
 
+-- !sql --
+123.321	{"col":1, "col1":12345.24}
+
+-- !sql --
+123.321	{"col":1, "col1":12345.24}
+

regression-test/suites/query_p0/sql_functions/struct_functions/test_struct_functions.groovy

@@ -47,4 +47,12 @@ suite("test_struct_functions") {
     qt_select_struct_element_2 "SELECT struct_element(k3,'f1'),struct_element(k3,'f2'),struct_element(k3,'f3') FROM ${tableName} ORDER BY k1"
     qt_select_struct_element_3 "SELECT struct_element(k4,1),struct_element(k4,2),struct_element(k4,3),struct_element(k4,4) FROM ${tableName} ORDER BY k1"
     qt_select_struct_element_4 "SELECT struct_element(k5,1),struct_element(k5,2),struct_element(k5,3) FROM ${tableName} ORDER BY k1"
+
+    //The precision of the decimal type in the test select is inconsistent with the precision of the function named_struct containing the decimal type.
+    sql """ drop table if exists t01 --force """;
+    sql """ create table if not exists t01 (a decimal(6,3), d struct<col:bigint, col1:decimal(7,2)>) properties ("replication_num"="1");"""
+    sql """ insert into t01 values (123.321, named_struct('col', 1, 'col1', 345.24));"""
+    qt_sql_before """ select named_struct("col_11", a, "col_12", d) from t01; """
+    sql """ insert into t01 values (123.321, named_struct('col', 1, 'col1', 12345.24));"""
+    qt_sql_after """ select named_struct("col_11", a, "col_12", d) from t01; """
 }

regression-test/suites/query_p0/sql_functions/struct_functions/test_struct_functions_by_literal.groovy

@@ -33,4 +33,8 @@ suite("test_struct_functions_by_literal") {
 
     qt_sql "select struct_element(named_struct('f1', 1, 'f2', 2, 'f3', 3), 'f1')"
     qt_sql "select struct_element(named_struct('f1', 1, 'f2', 1000, 'f3', 10000000000), 3)"
+
+    //The precision of the decimal type in the test select is inconsistent with the precision of the function named_struct containing the decimal type.
+    qt_sql "select cast(123.321 as decimal(6,3)), named_struct('col', 1, 'col1', 12345.24)"
+    qt_sql "select cast(123.321 as decimal(6,3)), named_struct('col', 1, 'col1', cast(12345.24 as decimal(7,2)))"
 }