[GitHub] [incubator-doris] HangyuanLiu commented on a change in pull request #4858: [BUG] Fix field error in information_schema.columns

[GitBox <gi...@apache.org>]

HangyuanLiu commented on a change in pull request #4858:
URL: https://github.com/apache/incubator-doris/pull/4858#discussion_r521182314



##########
File path: be/src/exec/schema_scanner/schema_columns_scanner.cpp
##########
@@ -250,20 +265,33 @@ Status SchemaColumnsScanner::fill_one_row(Tuple *tuple, MemPool *pool) {
         memcpy(str_slot->ptr, buffer.c_str(), str_slot->len);
     }
     // CHARACTER_MAXIMUM_LENGTH
+    // For string columns, the maximum length in characters.
     {
-        tuple->set_null(_tuple_desc->slots()[8]->null_indicator_offset());
+        int data_type = _desc_result.columns[_column_index].columnDesc.columnType;
+        if (data_type == TPrimitiveType::VARCHAR || data_type == TPrimitiveType::CHAR) {
+            void *slot = tuple->get_slot(_tuple_desc->slots()[8]->tuple_offset());
+            int64_t* str_slot = reinterpret_cast<int64_t*>(slot);
+            if (_desc_result.columns[_column_index].columnDesc.__isset.columnLength) {
+                *str_slot = _desc_result.columns[_column_index].columnDesc.columnLength;
+            } else {
+                tuple->set_null(_tuple_desc->slots()[8]->null_indicator_offset());
+            }
+        } else {
+            tuple->set_null(_tuple_desc->slots()[8]->null_indicator_offset());
+        }
     }
     // CHARACTER_OCTET_LENGTH
+    // For string columns, the maximum length in bytes.
     {
         int data_type = _desc_result.columns[_column_index].columnDesc.columnType;
         if (data_type == TPrimitiveType::VARCHAR || data_type == TPrimitiveType::CHAR) {
             void *slot = tuple->get_slot(_tuple_desc->slots()[9]->tuple_offset());
             int64_t* str_slot = reinterpret_cast<int64_t*>(slot);
             if (_desc_result.columns[_column_index].columnDesc.__isset.columnLength) {
-                *str_slot = _desc_result.columns[_column_index].columnDesc.columnLength;
+                *str_slot = _desc_result.columns[_column_index].columnDesc.columnLength * 4;

Review comment:
       For mysql-compatible purposes, we need to multiply this by 4. 
   According to https://dev.mysql.com/doc/refman/8.0/en/information-schema-columns-table.html. CHARACTER_OCTET_LENGTH stands for maximum length in **bytes**, while CHARACTER_MAXIMUM_LENGTH stands for maximum length in **characters**




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