通过Rfc4180CsvParser导入数据时，有没有办法排除标题行？ COPY命令具有SKIP选项，但在使用Vertica SDK中提供的CSV解析器时，该选项似乎不起作用。
背景
作为背景，COPY命令本身不会读取CSV文件。对于简单的CSV文件，可以说COPY schema.table FROM '/data/myfile.csv' DELIMITER ',' ENCLOSED BY '"';，但是对于具有带嵌入式引号的字符串值的数据文件，这将失败。
添加ESCAPE AS '"'会生成错误ERROR 3169: ENCLOSED BY and ESCAPE AS can not be the same value。这是一个问题，因为"包含并转义了CSV值。
Vertica SDK CsvParser救援扩展
Vertica在/opt/vertica/sdk/examples下提供了一个SDK，其中包含可编译为扩展的C ++程序。其中之一是/opt/vertica/sdk/examples/ParserFunctions/Rfc4180CsvParser.cpp。
这很有效，如下：
cd /opt/vertica/sdk/examples
make clean
vsql
==> CREATE LIBRARY Rfc4180CsvParserLib AS '/opt/vertica/sdk/examples/build/Rfc4180CsvParser.so';
==> COPY myschema.mytable FROM '/data/myfile.csv' WITH PARSER Rfc4180CsvParser();
问题
上面的除了以外，它将数据文件的第一行作为一行导入。 COPY命令有SKIP 1选项，但这不适用于解析器。
问题
是否可以编辑Rfc4180CsvParser.cpp以跳过第一行，或者更好的是，采用一些参数来指定要跳过的行数？
该程序只有135行，但我看不到在哪里/如何进行这个切口。提示？
复制下面的整个程序，因为我没有看到公共回购链接到...
Rfc4180CsvParser.cpp
/* Copyright (c) 2005 - 2012 Vertica, an HP company -*- C++ -*- */
#include "Vertica.h"
#include "StringParsers.h"
#include "csv.h"
using namespace Vertica;
// Note, the class template is mostly for demonstration purposes,
// so that the same class can use each of two string-parsers.
// Custom parsers can also just pick a string-parser to use.
/**
* A parser that parses something approximating the "official" CSV format
* as defined in IETF RFC-4180: <http://tools.ietf.org/html/rfc4180>
* Oddly enough, many "CSV" files don't actually conform to this standard
* for one reason or another. But for sources that do, this parser should
* be able to handle the data.
* Note that the CSV format does not specify how to handle different
* data types; it is entirely a string-based format.
* So we just use standard parsers based on the corresponding column type.
*/
template <class StringParsersImpl>
class LibCSVParser : public UDParser {
public:
LibCSVParser() : colNum(0) {}
// Keep a copy of the information about each column.
// Note that Vertica doesn't let us safely keep a reference to
// the internal copy of this data structure that it shows us.
// But keeping a copy is fine.
SizedColumnTypes colInfo;
// An instance of the class containing the methods that we're
// using to parse strings to the various relevant data types
StringParsersImpl sp;
/// Current column index
size_t colNum;
/// Parsing state for libcsv
struct csv_parser parser;
// Format strings
std::vector<std::string> formatStrings;
/**
* Given a field in string form (a pointer to the first character and
* a length), submit that field to Vertica.
* `colNum` is the column number from the input file; how many fields
* it is into the current record.
*/
bool handleField(size_t colNum, char* start, size_t len) {
if (colNum >= colInfo.getColumnCount()) {
// Ignore column overflow
return false;
}
// Empty colums are null.
if (len==0) {
writer->setNull(colNum);
return true;
} else {
return parseStringToType(start, len, colNum, colInfo.getColumnType(c
olNum), writer, sp);
}
}
static void handle_record(void *data, size_t len, void *p) {
static_cast<LibCSVParser*>(p)->handleField(static_cast<LibCSVParser*>(p)
->colNum++, (char*)data, len);
}
static void handle_end_of_row(int c, void *p) {
// Ignore 'c' (the terminating character); trust that it's correct
static_cast<LibCSVParser*>(p)->colNum = 0;
static_cast<LibCSVParser*>(p)->writer->next();
}
virtual StreamState process(ServerInterface &srvInterface, DataBuffer &input
, InputState input_state) {
size_t processed;
while ((processed = csv_parse(&parser, input.buf + input.offset, input.s
ize - input.offset,
handle_record, handle_end_of_row, this)) > 0) {
input.offset += processed;
}
if (input_state == END_OF_FILE && input.size == input.offset) {
csv_fini(&parser, handle_record, handle_end_of_row, this);
return DONE;
}
return INPUT_NEEDED;
}
virtual void setup(ServerInterface &srvInterface, SizedColumnTypes &returnTy
pe);
virtual void destroy(ServerInterface &srvInterface, SizedColumnTypes &return
Type) {
csv_free(&parser);
}
};
template <class StringParsersImpl>
void LibCSVParser<StringParsersImpl>::setup(ServerInterface &srvInterface, Sized
ColumnTypes &returnType) {
csv_init(&parser, CSV_APPEND_NULL);
colInfo = returnType;
}
template <>
void LibCSVParser<FormattedStringParsers>::setup(ServerInterface &srvInterface,
SizedColumnTypes &returnType) {
csv_init(&parser, CSV_APPEND_NULL);
colInfo = returnType;
if (formatStrings.size() != returnType.getColumnCount()) {
formatStrings.resize(returnType.getColumnCount(), "");
}
sp.setFormats(formatStrings);
}
template <class StringParsersImpl>
class LibCSVParserFactoryTmpl : public ParserFactory {
public:
virtual void plan(ServerInterface &srvInterface,
PerColumnParamReader &perColumnParamReader,
PlanContext &planCtxt) {}
virtual UDParser* prepare(ServerInterface &srvInterface,
PerColumnParamReader &perColumnParamReader,
PlanContext &planCtxt,
const SizedColumnTypes &returnType)
{
return vt_createFuncObj(srvInterface.allocator,
LibCSVParser<StringParsersImpl>);
}
};
typedef LibCSVParserFactoryTmpl<StringParsers> LibCSVParserFactory;
RegisterFactory(LibCSVParserFactory);
typedef LibCSVParserFactoryTmpl<FormattedStringParsers> FormattedLibCSVParserFac
tory;
RegisterFactory(FormattedLibCSVParserFactory);
答案 0 :(得分：2)
快速而肮脏的方式就是硬编码。它正在使用handle_end_of_row的回调。跟踪行号，只是不处理第一行。类似的东西：
static void handle_end_of_row(int c, void *ptr) {
// Ignore 'c' (the terminating character); trust that it's correct
LibCSVParser *p = static_cast<LibCSVParser*>(ptr);
p->colNum = 0;
if (rowcnt <= 0) {
p->bad_field = "";
rowcnt++;
} else if (p->bad_field.empty()) {
p->writer->next();
} else {
// libcsv doesn't give us the whole row to reject.
// So just write to the log.
// TODO: Come up with something more clever.
if (p->currSrvInterface) {
p->currSrvInterface->log("Invalid CSV field value: '%s' Row skipped.",
p->bad_field.c_str());
}
p->bad_field = "";
}
}
另外，最好在rownum = 0中初始化process，因为我认为它会为COPY语句中的每个文件调用此值。可能有更聪明的方法来做到这一点。基本上，这只会处理记录然后丢弃它。
至于支持SKIP一般......请查看TraditionalCSVParser如何处理参数传递。您必须将其添加到解析器因子prepare并将值发送到LibCSVParser类并覆盖getParameterType。然后在LibCSVParser中，您需要接受构造函数中的参数，并修改process以跳过第一个skip行。然后使用该值而不是上面的硬编码0。