我已经搜索并找到了一些与 postgres csv 导入相关的帖子，但没有解决我当前的问题。
我一直使用 postgres copy命令将来自异构数据源的数据带入我们的系统。目前正在努力处理 1 亿行 .csv 文件，逗号分隔。问题是这样的行：
009098,0981098094,"something","something else",""this one, well, is a problem"", "another thing"
用嵌入逗号的双引号括起来的字段。这些字段未正确解析，我收到错误消息：
"ERROR: extra data after last expected column"
通常当出现这种情况时，我会临时处理有问题的行，但是这个文件太大了，我希望有一些更通用的方法来防御它。要求修改数据格式是不可能的。
copy mytable from '/path/to/file.csv' csv header quote '"'
那是格式错误的 CSV。您将双引号加倍以在引号字段中嵌入双引号；例如：
"where","is ""pancakes""","house?"
具有三个值：
whereis "pancakes"house?您遇到问题的行有双引号：
009098,0981098094,"something","something else",""this one, well, is a problem"", "another thing"
^^ ^^
我认为COPY对此无能为力，因为正确的版本是模棱两可的：应该是"this one, well, is a problem"还是应该是"""this one, well, is a problem"""？
我认为你必须手动修复它。如果您可以唯一地识别损坏的行，那么一个快速sed的单行应该能够完成这项工作。
出于参考目的，我见过的最接近 CSV 标准的是RFC 4180，第二部分有这样的说法：
5. Each field may or may not be enclosed in double quotes (however
some programs, such as Microsoft Excel, do not use double quotes
at all). If fields are not enclosed with double quotes, then
double quotes may not appear inside the fields. For example:
"aaa","bbb","ccc" CRLF
zzz,yyy,xxx
[...]
7. If double-quotes are used to enclose fields, then a double-quote
appearing inside a field must be escaped by preceding it with
another double quote. For example:
"aaa","b""bb","ccc"
这是基于 Kernighan 和 Plauger的 The Practice of Programming中的 CSV 代码的代码，该代码已经适应处理您奇怪的格式错误的 CSV 数据。（这并不难；我已经完成了主要代码的工作和打包，所以我只需要添加 CSV 输出函数并修改advquoted()函数以处理这个问题中奇怪的格式。
/*
@(#)File: $RCSfile: csv2.h,v $
@(#)Version: $Revision: 2.1 $
@(#)Last changed: $Date: 2012/11/01 22:23:07 $
@(#)Purpose: Scanner for Comma Separated Variable (CSV) Data
@(#)Author: J Leffler
@(#)Origin: Kernighan & Pike, 'The Practice of Programming'
*/
/*TABSTOP=4*/
#ifndef CSV2_H
#define CSV2_H
#ifdef __cplusplus
extern "C" {
#endif
#ifdef MAIN_PROGRAM
#ifndef lint
/* Prevent over-aggressive optimizers from eliminating ID string */
const char jlss_id_csv2_h[] = "@(#)$Id: csv2.h,v 2.1 2012/11/01 22:23:07 jleffler Exp $";
#endif /* lint */
#endif /* MAIN_PROGRAM */
#include <stdio.h>
extern char *csvgetline(FILE *ifp); /* Read next input line */
extern char *csvgetfield(size_t n); /* Return field n */
extern size_t csvnfield(void); /* Return number of fields */
extern void csvreset(void); /* Release space used by CSV */
extern int csvputfield(FILE *ofp, const char *field);
extern int csvputline(FILE *ofp, char **fields, int nfields);
extern void csvseteol(const char *eol);
#ifdef __cplusplus
}
#endif
#endif /* CSV2_H */
/*
@(#)File: $RCSfile: csv2.c,v $
@(#)Version: $Revision: 2.1 $
@(#)Last changed: $Date: 2012/11/01 22:23:07 $
@(#)Purpose: Scanner for Comma Separated Variable (CSV) Data
@(#)Modification: Deal with specific malformed CSV
@(#)Author: J Leffler
@(#)Origin: Kernighan & Pike, 'The Practice of Programming'
*/
/*TABSTOP=4*/
#ifndef lint
/* Prevent over-aggressive optimizers from eliminating ID string */
const char jlss_id_csv2_c[] = "@(#)$Id: csv2.c,v 2.1 2012/11/01 22:23:07 jleffler Exp $";
#endif /* lint */
/*
** See RFC 4180 (http://www.ietf.org/rfc/rfc4180.txt).
**
** Specific malformed CSV - see SO 13183644 (http://stackoverflow.com/questions/13183644).
** Data contains malformed CSV fields like: OK,""this is a problem"",OK
** Two (but not three) field quotes at the start extract as "this is a problem" (with the quotes).
*/
#include "csv2.h"
#include <stdlib.h>
#include <string.h>
enum { NOMEM = -2 };
static char *line = 0; /* Input line */
static char *sline = 0; /* Split line */
static size_t maxline = 0; /* Size of line[] and sline[] */
static char **field = 0; /* Field pointers */
static size_t maxfield = 0; /* Size of field[] */
static size_t nfield = 0; /* Number of fields */
static char fieldsep[]= ","; /* Field separator characters */
static char fieldquote = '"'; /* Quote character */
static char eolstr[8] = "\n";
void csvreset(void)
{
free(line);
free(sline);
free(field);
line = 0;
sline = 0;
field = 0;
maxline = maxfield = nfield = 0;
}
static int endofline(FILE *ifp, int c)
{
int eol = (c == '\r' || c == '\n');
if (c == '\r')
{
c = getc(ifp);
if (c != '\n' && c != EOF)
ungetc(c, ifp);
}
return(eol);
}
/* Modified to deal with specific malformed CSV */
static char *advquoted(char *p)
{
size_t i;
size_t j;
if (p[0] == fieldquote && (p[1] != *fieldsep && p[1] != fieldquote))
{
/* Malformed CSV: ""some stuff"" --> "some stuff" */
/* Find "\"\"," or "\"\"\0" to mark end of field */
/* If we don't find it, drop through to 'regular' case */
char *eof = strstr(&p[2], "\"\"");
if (eof != 0 && (eof[2] == *fieldsep || eof[2] == '\0'))
{
p[eof + 1 - p] = '\0';
return(eof + 2);
}
}
for (i = j = 0; p[j] != '\0'; i++, j++)
{
if (p[j] == fieldquote && p[++j] != fieldquote)
{
size_t k = strcspn(p+j, fieldsep);
memmove(p+i, p+j, k); // 1 -> i fixing transcription error
i += k;
j += k;
break;
}
p[i] = p[j];
}
p[i] = '\0';
return(p + j);
}
static int split(void)
{
char *p;
char **newf;
char *sepp;
int sepc;
nfield = 0;
if (line[0] == '\0')
return(0);
strcpy(sline, line);
p = sline;
do
{
if (nfield >= maxfield)
{
maxfield *= 2;
newf = (char **)realloc(field, maxfield * sizeof(field[0]));
if (newf == 0)
return NOMEM;
field = newf;
}
if (*p == fieldquote)
sepp = advquoted(++p);
else
sepp = p + strcspn(p, fieldsep);
sepc = sepp[0];
sepp[0] = '\0';
field[nfield++] = p;
p = sepp + 1;
} while (sepc == ',');
return(nfield);
}
char *csvgetline(FILE *ifp)
{
size_t i;
int c;
if (line == NULL)
{
/* Allocate on first call */
maxline = maxfield = 1;
line = (char *)malloc(maxline); /*=C++=*/
sline = (char *)malloc(maxline); /*=C++-*/
field = (char **)malloc(maxfield*sizeof(field[0])); /*=C++=*/
if (line == NULL || sline == NULL || field == NULL)
{
csvreset();
return(NULL); /* out of memory */
}
}
for (i = 0; (c = getc(ifp)) != EOF && !endofline(ifp, c); i++)
{
if (i >= maxline - 1)
{
char *newl;
char *news;
maxline *= 2;
newl = (char *)realloc(line, maxline); /*=C++=*/
news = (char *)realloc(sline, maxline); /*=C++-*/
if (newl == NULL || news == NULL)
{
csvreset();
return(NULL); /* out of memory */
}
line = newl;
sline = news;
}
line[i] = c;
}
line[i] = '\0';
if (split() == NOMEM)
{
csvreset();
return(NULL);
}
return((c == EOF && i == 0) ? NULL : line);
}
char *csvgetfield(size_t n)
{
if (n >= nfield)
return(0);
return(field[n]);
}
size_t csvnfield(void)
{
return(nfield);
}
int csvputfield(FILE *ofp, const char *ofield)
{
const char escapes[] = "\",\r\n";
if (strpbrk(ofield, escapes) != 0)
{
size_t len = strlen(ofield) + 2;
const char *pos = ofield;
while ((pos = strchr(pos, '"')) != 0)
{
len++;
pos++;
}
char *space = malloc(len+1);
if (space == 0)
return EOF;
char *cpy = space;
pos = ofield;
*cpy++ = '"';
char c;
while ((c = *pos++) != '\0')
{
if (c == '"')
*cpy++ = c;
*cpy++ = c;
}
*cpy++ = '"';
*cpy = '\0';
int rc = fputs(space, ofp);
free(space);
return rc;
}
else
return fputs(ofield, ofp);
}
int csvputline(FILE *ofp, char **fields, int nfields)
{
for (int i = 0; i < nfields; i++)
{
if (i > 0)
putc(',', ofp);
if (csvputfield(ofp, fields[i]) == EOF)
return EOF;
}
return(fputs(eolstr, ofp));
}
void csvseteol(const char *eol)
{
size_t nbytes = strlen(eol);
if (nbytes >= sizeof(eolstr))
nbytes = sizeof(eolstr) - 1;
memmove(eolstr, eol, nbytes);
eolstr[nbytes] = '\0';
}
#ifdef TEST
int main(void)
{
char *in_line;
while ((in_line = csvgetline(stdin)) != 0)
{
size_t n = csvnfield();
char *fields[n]; /* C99 VLA */
printf("line = '%s'\n", in_line);
for (size_t i = 0; i < n; i++)
{
printf("field[%zu] = '%s'\n", i, csvgetfield(i));
printf("field[%zu] = [", i);
csvputfield(stdout, csvgetfield(i));
fputs("]\n", stdout);
fields[i] = csvgetfield(i);
}
printf("fields[0..%zu] = ", n-1);
csvputline(stdout, fields, n);
}
return(0);
}
#endif /* TEST */
编译代码以使用示例函数-DTEST创建程序。main()你需要一个 C99 编译器；中的代码main()使用 VLA（可变长度数组）。您可以通过动态内存分配或悲观（过度杀伤）内存分配来避免这种情况（几千个指针的数组现在不会杀死大多数系统，但很少有 CSV 文件每行会有几千个字段）。
密切基于问题中的数据。
009098,0981098094,"something","something else",""this one, well, is a problem"", "another thing"
123458,1234561007,"anything","nothing else",""this one, well, is a problem"","dohicky
503458,1234598094,"nothing","everything else","""this one, well, it isn't a problem""","abelone"
610078,1236100794,"everything","anything else","this ""isn't a problem"", he said.","Orcas Rule"
line = '009098,0981098094,"something","something else",""this one, well, is a problem"", "another thing"'
field[0] = '009098'
field[0] = [009098]
field[1] = '0981098094'
field[1] = [0981098094]
field[2] = 'something'
field[2] = [something]
field[3] = 'something else'
field[3] = [something else]
field[4] = '"this one, well, is a problem"'
field[4] = ["""this one, well, is a problem"""]
field[5] = ' "another thing"'
field[5] = [" ""another thing"""]
fields[0..5] = 009098,0981098094,something,something else,"""this one, well, is a problem"""," ""another thing"""
line = '123458,1234561007,"anything","nothing else",""this one, well, is a problem"","dohicky'
field[0] = '123458'
field[0] = [123458]
field[1] = '1234561007'
field[1] = [1234561007]
field[2] = 'anything'
field[2] = [anything]
field[3] = 'nothing else'
field[3] = [nothing else]
field[4] = '"this one, well, is a problem"'
field[4] = ["""this one, well, is a problem"""]
field[5] = 'dohicky'
field[5] = [dohicky]
fields[0..5] = 123458,1234561007,anything,nothing else,"""this one, well, is a problem""",dohicky
line = '503458,1234598094,"nothing","everything else","""this one, well, it isn't a problem""","abelone"'
field[0] = '503458'
field[0] = [503458]
field[1] = '1234598094'
field[1] = [1234598094]
field[2] = 'nothing'
field[2] = [nothing]
field[3] = 'everything else'
field[3] = [everything else]
field[4] = '"this one, well, it isn't a problem"'
field[4] = ["""this one, well, it isn't a problem"""]
field[5] = 'abelone'
field[5] = [abelone]
fields[0..5] = 503458,1234598094,nothing,everything else,"""this one, well, it isn't a problem""",abelone
line = '610078,1236100794,"everything","anything else","this ""isn't a problem"", he said.","Orcas Rule"'
field[0] = '610078'
field[0] = [610078]
field[1] = '1236100794'
field[1] = [1236100794]
field[2] = 'everything'
field[2] = [everything]
field[3] = 'anything else'
field[3] = [anything else]
field[4] = 'this "isn't a problem", he said.'
field[4] = ["this ""isn't a problem"", he said."]
field[5] = 'Orcas Rule'
field[5] = [Orcas Rule]
fields[0..5] = 610078,1236100794,everything,anything else,"this ""isn't a problem"", he said.",Orcas Rule
字段打印两次，一次测试字段提取，一次测试字段打印。csvputline()除了将文件从格式错误的 CSV 转换为格式正确的 CSV之外，您可以通过删除打印来简化输出。