Bug fix for csv input field empty

src/Core/Settings.h

@@ -943,6 +943,7 @@ class IColumn;
     M(Bool, input_format_import_nested_json, false, "Map nested JSON data to nested tables (it works for JSONEachRow format).", 0) \
     M(Bool, input_format_defaults_for_omitted_fields, true, "For input data calculate default expressions for omitted fields (it works for JSONEachRow, -WithNames, -WithNamesAndTypes formats).", IMPORTANT) \
     M(Bool, input_format_csv_empty_as_default, true, "Treat empty fields in CSV input as default values.", 0) \
+    M(Bool, input_format_csv_default_empty_for_nullable_string, false, "Treat empty as default value for nullable string field.", 0) \
     M(Bool, input_format_tsv_empty_as_default, false, "Treat empty fields in TSV input as default values.", 0) \
     M(Bool, input_format_tsv_enum_as_number, false, "Treat inserted enum values in TSV formats as enum indices.", 0) \
     M(Bool, input_format_null_as_default, true, "Initialize null fields with default values if the data type of this field is not nullable and it is supported by the input format", 0) \

src/Formats/FormatFactory.cpp

@@ -66,6 +66,7 @@ FormatSettings getFormatSettings(ContextPtr context, const Settings & settings)
     format_settings.csv.empty_as_default = settings.input_format_csv_empty_as_default;
     format_settings.csv.enum_as_number = settings.input_format_csv_enum_as_number;
     format_settings.csv.null_representation = settings.format_csv_null_representation;
+    format_settings.csv.default_empty_for_nullable_string = settings.input_format_csv_default_empty_for_nullable_string;
     format_settings.csv.arrays_as_nested_csv = settings.input_format_csv_arrays_as_nested_csv;
     format_settings.csv.use_best_effort_in_schema_inference = settings.input_format_csv_use_best_effort_in_schema_inference;
     format_settings.csv.skip_first_lines = settings.input_format_csv_skip_first_lines;

src/Formats/FormatSettings.h

@@ -152,6 +152,7 @@ struct FormatSettings
         char delimiter = ',';
         bool allow_single_quotes = true;
         bool allow_double_quotes = true;
+        bool default_empty_for_nullable_string = false;
         bool empty_as_default = false;
         bool crlf_end_of_line = false;
         bool allow_cr_end_of_line = false;

src/Processors/Formats/Impl/CSVRowInputFormat.cpp

@@ -367,10 +367,11 @@ bool CSVFormatReader::readField(
 
     const bool at_delimiter = !buf->eof() && *buf->position() == format_settings.csv.delimiter;
     const bool at_last_column_line_end = is_last_file_column && (buf->eof() || *buf->position() == '\n' || *buf->position() == '\r');
+    const bool nullable_string_field_as_empty = format_settings.csv.default_empty_for_nullable_string && type->isNullable() && isString(removeNullable(type));
 
     /// Note: Tuples are serialized in CSV as separate columns, but with empty_as_default or null_as_default
     /// only one empty or NULL column will be expected
-    if (format_settings.csv.empty_as_default && (at_delimiter || at_last_column_line_end))
+    if (format_settings.csv.empty_as_default && (at_delimiter || at_last_column_line_end) && !nullable_string_field_as_empty)
     {
         /// Treat empty unquoted column value as default value, if
         /// specified in the settings. Tuple columns might seem