绑定参数如何在 SQLite3 中工作（以最小的例子为例）？

Question

有人建议在 SQLite 中使用参数绑定来加速重复查询。但是，如果我有多个用于绑定的参数，则它不起作用。我没有看到我的错误。所有 SQLite 函数都返回 SQLITE_OK...

下面，我写了一个最小的例子。它创建一个表，创建三个条目，然后查询两次，一次使用一个绑定参数，一次使用两个。第一次返回一个结果，这是正确的。第二个返回零结果，而 sqlite3_step() 返回 101 (SQLITE_DONE)。为什么它也不返回一个结果？

#include <vector>
#include <sqlite3.h>

int main(int argc, char * argv[])
{
  sqlite3 * pDB;
  int iReturn = sqlite3_open("./Test.db", &pDB);
  if (iReturn != SQLITE_OK) {
    return 1;
  }

  // create table
  {
    std::string str = "CREATE TABLE Names(ID INTEGER PRIMARY KEY, Name VARCHAR(30))";
    iReturn = sqlite3_exec(pDB, str.c_str(), NULL, NULL, NULL);
    if (iReturn != SQLITE_OK) {
      sqlite3_close(pDB);
      return 1;
    }
  }

  // insert data using binding
  {
    std::string str = "INSERT INTO Names(Name) VALUES(?)";
    sqlite3_stmt * pStmt = nullptr;

    iReturn = sqlite3_prepare_v2(pDB, str.c_str(), str.size() + 1, &pStmt, nullptr);
    if (iReturn != SQLITE_OK) {
      sqlite3_close(pDB);
      return 1;
    }

    printf("The statement %s has %d parameter(s).\n", str.c_str(), sqlite3_bind_parameter_count(pStmt));

    std::vector<std::string> vecNames;
    vecNames.push_back("Smith");
    vecNames.push_back("Morpheus");
    vecNames.push_back("Neo");

    for (unsigned int i = 0, iEnd = vecNames.size(); i != iEnd; ++i)
    {
      iReturn = sqlite3_bind_text(pStmt, 1, vecNames[i].c_str(), vecNames[i].size() + 1, nullptr);
      if (iReturn != SQLITE_OK) {
        return 1;
      }

      if (sqlite3_step(pStmt) != SQLITE_DONE) {
        sqlite3_finalize(pStmt);
        sqlite3_close(pDB);
        return 1;
      }

      sqlite3_reset(pStmt);
      sqlite3_clear_bindings(pStmt);
    }

  }

  // query using one bind parameter
  {
    sqlite3_stmt * pStmt = nullptr;
    string str = "SELECT ID FROM Names WHERE Name=?1";
    iReturn = sqlite3_prepare_v2(pDB, str.c_str(), str.size() + 1, &pStmt, nullptr);
    if (iReturn != SQLITE_OK) {
      return 1;
    }

    printf("The statement %s has %d parameters(s).\n", str.c_str(), sqlite3_bind_parameter_count(pStmt));

    // fourth parameter is length = position of \0
    iReturn = sqlite3_bind_text(pStmt, 1, "Neo", 3, NULL);
    if (iReturn != SQLITE_OK) {
      return 1;
    }

    vector<string> vecResults;
    char cBuffer[1024];
    string strBuffer;
    while (sqlite3_step(pStmt) == SQLITE_ROW)
    {
      sprintf(cBuffer, "%s", sqlite3_column_text(pStmt, 0));
      strBuffer = cBuffer;
      vecResults.push_back(strBuffer);
    }

    sqlite3_finalize(pStmt);

    printf("Found %d results.\n", vecResults.size());
    for (unsigned int i = 0, iEnd = vecResults.size(); i != iEnd; ++i)
    {
      printf("%d: %s\n", i, vecResults[i].c_str());
    }
  }

  // query using two bind parameters
  {
    sqlite3_stmt * pStmt = nullptr;
    string str = "SELECT ID FROM Names WHERE Name=?1 AND ID=?2";
    iReturn = sqlite3_prepare_v2(pDB, str.c_str(), str.size() + 1, &pStmt, nullptr);
    if (iReturn != SQLITE_OK) {
      return 1;
    }

    printf("The statement %s has %d parameters(s).\n", str.c_str(), sqlite3_bind_parameter_count(pStmt));

    // fourth parameter is length = position of \0
    iReturn = sqlite3_bind_text(pStmt, 1, "Neo", 3, NULL);
    if (iReturn != SQLITE_OK) {
      return 1;
    }


    iReturn = sqlite3_bind_text(pStmt, 2, "3", 2, NULL);
    if (iReturn != SQLITE_OK) {
      return 1;
    }


    vector<string> vecResults;
    char cBuffer[1024];
    string strBuffer;
    while (sqlite3_step(pStmt) == SQLITE_ROW)
    {
      sprintf(cBuffer, "%s", sqlite3_column_text(pStmt, 0));
      strBuffer = cBuffer;
      vecResults.push_back(strBuffer);
    }

    sqlite3_finalize(pStmt);

    printf("Found %d results.\n", vecResults.size());
    for (unsigned int i = 0, iEnd = vecResults.size(); i != iEnd; ++i)
    {
      printf("%d: %s\n", i, vecResults[i].c_str());
    }
  }

  sqlite3_close(pDB);

  return 0;
}

Answer 1

因为行不是字符串。

将第二个参数的绑定更改为sqlite3_bind_int(pStmt, 2, 3);，它应该可以正常工作。

另外，为什么您的姓名行为 VARCHAR(30) 而不是 TEXT？