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src/sql/engine/expr/ob_expr_left.cpp

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+/**
+ * Copyright (c) 2021 OceanBase
+ * OceanBase CE is licensed under Mulan PubL v2.
+ * You can use this software according to the terms and conditions of the Mulan PubL v2.
+ * You may obtain a copy of Mulan PubL v2 at:
+ *          http://license.coscl.org.cn/MulanPubL-2.0
+ * THIS SOFTWARE IS PROVIDED ON AN "AS IS" BASIS, WITHOUT WARRANTIES OF ANY KIND,
+ * EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO NON-INFRINGEMENT,
+ * MERCHANTABILITY OR FIT FOR A PARTICULAR PURPOSE.
+ * See the Mulan PubL v2 for more details.
+ */
+
+#define USING_LOG_PREFIX SQL_ENG
+#include "sql/engine/expr/ob_expr_left.h"
+#include "lib/charset/ob_charset.h"
+#include "sql/session/ob_sql_session_info.h"
+
+using namespace oceanbase::common;
+using namespace oceanbase::sql;
+
+namespace oceanbase {
+namespace sql {
+
+ObExprLeft::ObExprLeft(ObIAllocator& alloc) : ObStringExprOperator(alloc, T_FUN_SYS_LEFT, "left", 2)
+{}
+
+ObExprLeft::~ObExprLeft()
+{}
+
+int ObExprLeft::calc_result_type2(
+    ObExprResType& type, ObExprResType& type1, ObExprResType& type2, ObExprTypeCtx& type_ctx) const
+{
+  int ret = OB_SUCCESS;
+  type2.set_calc_type(ObIntType);
+  type_ctx.set_cast_mode(type_ctx.get_cast_mode() | CM_STRING_INTEGER_TRUNC);
+  type.set_varchar();
+  type.set_length(type1.get_length());
+  OZ(aggregate_charsets_for_string_result(type, &type1, 1, type_ctx.get_coll_type()));
+  OX(type1.set_calc_type(ObVarcharType));
+  OX(type1.set_calc_collation_type(type.get_collation_type()));
+  return ret;
+}
+
+int calc_left(ObString& res_str, const ObString& text, const ObCollationType type, const int64_t required_num_char)
+{
+  int ret = OB_SUCCESS;
+  const char* str_ptr = text.ptr();
+  int64_t str_length = text.length();
+  if (OB_ISNULL(str_ptr) && 0 != str_length) {
+    ret = OB_INVALID_ARGUMENT;
+    LOG_WARN("invalid argument", K(ret));
+  } else {
+    int64_t input_num_char = ObCharset::strlen_char(type, text.ptr(), text.length());
+    int64_t expected_num_char = min(required_num_char, input_num_char);
+    int64_t start_pos = 0;
+    int64_t char_length = 0;
+    while ((start_pos < str_length) && OB_SUCC(ret) && (0 < expected_num_char)) {
+      if (OB_FAIL(ObCharset::first_valid_char(type, str_ptr + start_pos, str_length - start_pos, char_length))) {
+        LOG_WARN("get char failed", K(ret));
+      } else {
+        start_pos += char_length;
+        --expected_num_char;
+      }
+    }
+    if (OB_SUCC(ret)) {
+      res_str.assign_ptr(str_ptr, static_cast<int32_t>(start_pos));
+    }
+  }
+  return ret;
+}
+
+int ObExprLeft::calc_result2(ObObj& result, const ObObj& obj1, const ObObj& obj2, ObExprCtx& expr_ctx) const
+{
+  int ret = OB_SUCCESS;
+  if (OB_ISNULL(expr_ctx.calc_buf_)) {
+    ret = OB_NOT_INIT;
+    LOG_WARN("varchar buffer not init", K(ret));
+  } else if (obj1.is_null() || obj2.is_null()) {
+    result.set_null();
+  } else {
+    TYPE_CHECK(obj1, ObVarcharType);
+    TYPE_CHECK(obj2, ObIntType);
+    ObString res_str;
+    if (OB_FAIL(calc_left(res_str, obj1.get_string(), obj1.get_collation_type(), obj2.get_int()))) {
+      LOG_WARN("failed to calculate left expression", K(ret));
+    } else {
+      result.set_varchar(res_str);
+      result.set_collation(result_type_);
+    }
+  }
+  return ret;
+}
+
+int calc_left_expr(const ObExpr& expr, ObEvalCtx& ctx, ObDatum& res_datum)
+{
+  int ret = OB_SUCCESS;
+  // left(s, n)
+  ObDatum* s_datum = NULL;
+  ObDatum* n_datum = NULL;
+  if (OB_FAIL(expr.args_[0]->eval(ctx, s_datum)) || OB_FAIL(expr.args_[1]->eval(ctx, n_datum))) {
+    LOG_WARN("eval arg failed", K(ret), KP(s_datum), KP(n_datum));
+  } else if (s_datum->is_null() || n_datum->is_null()) {
+    res_datum.set_null();
+  } else {
+    // res_str will point to the memory space of s_datum, so the string pointed to
+    // by res_str cannot be changed below
+    ObString res_str;
+    const ObCollationType arg_cs_type = expr.args_[0]->datum_meta_.cs_type_;
+    if (OB_FAIL(calc_left(res_str, s_datum->get_string(), arg_cs_type, n_datum->get_int()))) {
+      LOG_WARN("failed to calculate left expression", K(ret));
+    } else {
+      if (res_str.empty() && is_oracle_mode()) {
+        res_datum.set_null();
+      } else {
+        res_datum.set_string(res_str);
+      }
+    }
+  }
+  return ret;
+}
+
+int ObExprLeft::cg_expr(ObExprCGCtx& expr_cg_ctx, const ObRawExpr& raw_expr, ObExpr& rt_expr) const
+{
+  int ret = OB_SUCCESS;
+  UNUSED(expr_cg_ctx);
+  UNUSED(raw_expr);
+  rt_expr.eval_func_ = calc_left_expr;
+  return ret;
+}
+
+} /* namespace sql */
+} /* namespace oceanbase */