CODEWITHSUNDEEP
mysqlc
Taavi
Taavi

Reputation: 101

MySQL C API - What is the return value of query that returns zero rows

I am using MySQL C API with my C program and trying to figure out, how to check if query returns zero rows. Got any tips?

Thanks in advance

Upvotes: 0

Views: 373

Answers (1)

kiran Biradar
kiran Biradar

Reputation: 12732

From developer mysql c-api-function-overview

After each mysql_query() (or mysql_real_query()). If the result set call succeeds, the statement was a SELECT and you can read the rows. If the result set call fails, call mysql_field_count() to determine whether a result was actually to be expected. If mysql_field_count() returns zero, the statement returned no data (indicating that it was an INSERT, UPDATE, DELETE, and so forth), and was not expected to return rows. If mysql_field_count() is nonzero, the statement should have returned rows, but did not. This indicates that the statement was a SELECT that failed. See the description for mysql_field_count() for an example of how this can be done.

You can use

unsigned int mysql_field_count(MYSQL *mysql)

to check the result of most recent query and take action accordingly.

Example from developper.mysql

MYSQL_RES *result;
unsigned int num_fields;
unsigned int num_rows;

if (mysql_query(&mysql,query_string))
{
    // error
}
else // query succeeded, process any data returned by it
{
    result = mysql_store_result(&mysql);
    if (result)  // there are rows
    {
        num_fields = mysql_num_fields(result);
        // retrieve rows, then call mysql_free_result(result)
    }
    else  // mysql_store_result() returned nothing; should it have?
    {
        if(mysql_field_count(&mysql) == 0)
        {
            // query does not return data
            // (it was not a SELECT)
            num_rows = mysql_affected_rows(&mysql);
        }
        else // mysql_store_result() should have returned data
        {
            fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
        }
    }
}

Upvotes: 2

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