From 9e297b88eaed65cd433e8bd99974e29421dc595c Mon Sep 17 00:00:00 2001
From: AntiTopQuark <AntiTopQuark1350@outlook.com>
Date: Sat, 28 Jan 2023 15:29:36 +0800
Subject: [PATCH] refresh mysqltest of weight_string expr

---
 src/sql/engine/expr/ob_expr_weight_string.cpp | 26 ++++++++++++++-----
 1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/src/sql/engine/expr/ob_expr_weight_string.cpp b/src/sql/engine/expr/ob_expr_weight_string.cpp
index 4789f2aa00..c2c5528c11 100644
--- a/src/sql/engine/expr/ob_expr_weight_string.cpp
+++ b/src/sql/engine/expr/ob_expr_weight_string.cpp
@@ -62,7 +62,7 @@ int ObExprWeightString::calc_result_typeN(ObExprResType &type,
       if (types_stack[0].get_type() > ObUNumberType &&
           types_stack[0].get_type() != ObBitType &&
           types_stack[0].get_type() != ObYearType) {
-        // 输入不是数字类型时
+        // When the input is not a numeric type, convert to a varchar type
         type_ctx.set_cast_mode(type_ctx.get_cast_mode() | CM_NULL_ON_WARN);
         types_stack[0].set_calc_type(ObVarcharType);
       }
@@ -73,18 +73,17 @@ int ObExprWeightString::calc_result_typeN(ObExprResType &type,
         types_stack[0].get_type() == ObTimestampType || 
         types_stack[0].get_type() == ObDateType ||
         types_stack[0].get_type() == ObTimeType ) {
-      // 日期、时间等类型，max_lenght是输入的类型的长度
+      // For types such as date, time, etc., the max_lenght is the length of the type entered
       max_length = types_stack[0].get_length();
     } else if (result_length > 0) {
       max_length = result_length;
     } else if (as_binary) {
-      // as_binary的情况下，以nweight作为输出结果的max_length
+      // In the case of as_binary, the max_length with nweight as the output result
       max_length = nweight; 
     } else {
-      // 输入为 char的情况下，使用cs->mbmaxlen计算max_length
+      // If the input is others, use cs->mbmaxlen to calculate the max_length
       max_length = cs->mbmaxlen * MAX(nweight, types_stack[0].get_length()*cs->mbmaxlen);
     }
-    // 推导结果
     type.set_varchar();
     type.set_collation_type(CS_TYPE_BINARY);
     type.set_collation_level(coll_level);
@@ -121,7 +120,6 @@ int ObExprWeightString::eval_weight_string(const ObExpr &expr, ObEvalCtx &ctx, O
     int64_t max_allowed_packet = 0;
     ObSQLSessionInfo *session = ctx.exec_ctx_.get_my_session();
     if (arg->is_null()) {
-      // The input string is NULL
       res_datum.set_null();
     } else if (!as_binary && (expr.args_[0]->datum_meta_.type_ <= ObUNumberType ||
                               expr.args_[0]->datum_meta_.type_ == ObBitType ||
@@ -156,6 +154,7 @@ int ObExprWeightString::eval_weight_string(const ObExpr &expr, ObEvalCtx &ctx, O
         tmp_length = cs->coll->strnxfrmlen(cs, cs->mbmaxlen*MAX(str.length() , nweights));
       }
       if (tmp_length >= max_allowed_packet) {
+        // The return result exceeds the maximum limit and returns NULL.
         res_datum.set_null();
       } else {
         int used_nweights = nweights;
@@ -169,14 +168,27 @@ int ObExprWeightString::eval_weight_string(const ObExpr &expr, ObEvalCtx &ctx, O
         }
         bool is_valid_unicode_tmp = 1;
         char *out_buf = expr.get_str_res_mem(ctx, tmp_length);
+        // For the case where the input is an empty string but the nweight is not 0,
+        // the weight_string function will call strnxfrm() to padding the result
+        // eg:
+        // mysql> select HEX(WEIGHT_STRING('' as char(3)));
+        // +-----------------------------------+
+        // | HEX(WEIGHT_STRING('' as char(3))) |
+        // +-----------------------------------+
+        // | 002000200020                      |
+        // +-----------------------------------+
+        // However, the strnxfrm requires that the input cannot be a null ptr,
+        // so an empty string is set as the input.
+        const char* tmp_empty_str = "";
         if (OB_ISNULL(out_buf)) {
           ret = OB_ALLOCATE_MEMORY_FAILED;
+          LOG_WARN("failed to alloc output buf",K(ret));
         } else {
           frm_length = cs->coll->strnxfrm(cs,
                                         reinterpret_cast<uchar *>(out_buf),
                                         tmp_length,
                                         used_nweights,
-                                        reinterpret_cast<const uchar *>(str.ptr()),
+                                        str.ptr() != NULL? reinterpret_cast<const uchar *>(str.ptr()) : reinterpret_cast<const uchar *>(tmp_empty_str),
                                         input_length,
                                         flags,
                                         &is_valid_unicode_tmp);