[Function] Let "str_to_date" return correct type

be/src/exprs/timestamp_functions.cpp

@@ -203,6 +203,26 @@ DateTimeVal TimestampFunctions::str_to_date(FunctionContext* ctx, const StringVa
                                        str.len)) {
         return DateTimeVal::null();
     }
+
+    /// The return type of str_to_date depends on whether the time part is included in the format.
+    /// If included, it is datetime, otherwise it is date.
+    /// If the format parameter is not constant, the return type will be datetime.
+    /// The above judgment has been completed in the FE query planning stage,
+    /// so here we directly set the value type to the return type set in the query plan.
+    ///
+    /// For example:
+    /// A table with one column k1 varchar, and has 2 lines:
+    ///     "%Y-%m-%d"
+    ///     "%Y-%m-%d %H:%i:%s"
+    /// Query:
+    ///     SELECT str_to_date("2020-09-01", k1) from tbl;
+    /// Result will be:
+    ///     2020-09-01 00:00:00
+    ///     2020-09-01 00:00:00
+    if (ctx->impl()->get_return_type().type == doris_udf::FunctionContext::Type::TYPE_DATETIME) {
+        ts_value.to_datetime();
+    }
+
     DateTimeVal ts_val;
     ts_value.to_datetime_val(&ts_val);
     return ts_val;

be/src/udf/udf_internal.h

@@ -102,6 +102,8 @@ class FunctionContextImpl {
 
     std::string& string_result() { return _string_result; }
 
+    const doris_udf::FunctionContext::TypeDesc& get_return_type() const { return _return_type; } 
+
 private:
     friend class doris_udf::FunctionContext;
     friend class ExprContext;

fe/fe-core/src/main/java/org/apache/doris/analysis/DateLiteral.java

@@ -498,14 +498,18 @@ public static DateLiteral dateParser(String date, String pattern) throws Analysi
                 dateTime.getHourOfDay(),
                 dateTime.getMinuteOfHour(),
                 dateTime.getSecondOfMinute());
-        if(HAS_TIME_PART.matcher(pattern).matches()) {
+        if (HAS_TIME_PART.matcher(pattern).matches()) {
             dateLiteral.setType(Type.DATETIME);
         } else {
             dateLiteral.setType(Type.DATE);
         }
         return dateLiteral;
     }
 
+    public static boolean hasTimePart(String format) {
+        return HAS_TIME_PART.matcher(format).matches();
+    }
+
     //Return the date stored in the dateliteral as pattern format.
     //eg : "%Y-%m-%d" or "%Y-%m-%d %H:%i:%s"
     public String dateFormat(String pattern) throws AnalysisException {

fe/fe-core/src/main/java/org/apache/doris/analysis/FunctionCallExpr.java

@@ -646,7 +646,46 @@ public void analyzeImpl(Analyzer analyzer) throws AnalysisException {
                 }
             }
         }
-        this.type = fn.getReturnType();
+
+        /**
+         * The return type of str_to_date depends on whether the time part is included in the format.
+         * If included, it is datetime, otherwise it is date.
+         * If the format parameter is not constant, the return type will be datetime.
+         * The above judgment has been completed in the FE query planning stage,
+         * so here we directly set the value type to the return type set in the query plan.
+         *
+         * For example:
+         * A table with one column k1 varchar, and has 2 lines:
+         *     "%Y-%m-%d"
+         *     "%Y-%m-%d %H:%i:%s"
+         * Query:
+         *     SELECT str_to_date("2020-09-01", k1) from tbl;
+         * Result will be:
+         *     2020-09-01 00:00:00
+         *     2020-09-01 00:00:00
+         *
+         * Query:
+         *      SELECT str_to_date("2020-09-01", "%Y-%m-%d");
+         * Return type is DATE
+         *
+         * Query:
+         *      SELECT str_to_date("2020-09-01", "%Y-%m-%d %H:%i:%s");
+         * Return type is DATETIME
+         */
+        if (fn.getFunctionName().getFunction().equals("str_to_date")) {
+            Expr child1Result = getChild(1).getResultValue();
+            if (child1Result instanceof StringLiteral) {
+                if (DateLiteral.hasTimePart(((StringLiteral) child1Result).getStringValue())) {
+                    this.type = Type.DATETIME;
+                } else {
+                    this.type = Type.DATE;
+                }
+            } else {
+                this.type = Type.DATETIME;
+            }
+        } else {
+            this.type = fn.getReturnType();
+        }
     }
 
     @Override
@@ -734,3 +773,4 @@ public int hashCode() {
         return result;
     }
 }
+