I am using prepared statements with the MYSQL C API and I am having trouble with truncation. mysql_stmt_fetch() always returns MYSQL_DATA_TRUNCATED and I don't understand why. Can someone give me reasons why the data would be truncated to help me troubleshoot this problem? The only reason I can think of is if my buffer variables were not of the right type, but I think they are the correct type. If you are interested, the code I am using is below. I also have shown a copy of my table and its structure, which I took directly from commands in the MYSQL client.
Some Notes about the code:
I have modified it to print out the values even when it returns truncated data. When I do so, the first field seems to print correctly, but the float field and datetime field are garbled. In addition, it seems to read the correct number of rows.
A majority of the code is error checking the various function calls. None of these error checks are triggered - or at least none of them print out messages as you would expect. The only indication of error is the MYSQL_DATA_TRUNCATED value returned by the fetch call.
Describe Measurements Table:
+------------+----------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+------------+----------+------+-----+---------+-------+
| nodeId | int(11) | NO | PRI | NULL | |
| recordtime | datetime | NO | PRI | NULL | |
| slevel | float | YES | | NULL | |
+------------+----------+------+-----+---------+-------+
Current Contents of Measurements Table:
+--------+---------------------+--------+
| nodeId | recordtime | slevel |
+--------+---------------------+--------+
| 1 | 2015-09-22 19:33:50 | 2 |
| 1 | 2015-09-24 21:10:20 | 2 |
| 2 | 2015-09-22 19:33:53 | 5 |
| 3 | 2015-09-22 19:33:55 | 2 |
| 3 | 2015-09-22 19:45:42 | 4 |
| 3 | 2015-09-24 21:12:12 | 2 |
| 3 | 2015-09-24 21:13:30 | 3.4 |
| 4 | 2015-09-22 19:33:57 | 7 |
| 4 | 2015-09-24 21:05:53 | 5 |
| 4 | 2015-09-24 21:07:27 | 3 |
| 4 | 2015-09-24 21:22:52 | 9.9 |
| 4 | 2015-09-24 21:35:53 | 5 |
| 6 | 2015-09-24 21:26:01 | 2.2 |
| 6 | 2015-09-24 21:28:15 | 5.4 |
+--------+---------------------+--------+
14 rows in set (0.00 sec)
My Code:
static void select_rows (MYSQL_STMT *stmt){
char *stmt_str = "SELECT nodeId, recordtime, slevel FROM Measurements";
MYSQL_BIND param[3];
int my_int;
float my_float;
MYSQL_TIME my_datetime;
my_bool is_null[3];
if (mysql_stmt_prepare (stmt, stmt_str, strlen (stmt_str)) != 0){
print_stmt_error (stmt, "Could not prepare SELECT statement");
return;}
if (mysql_stmt_field_count (stmt) != 3){
print_stmt_error (stmt, "Unexpected column count from SELECT");
return;}
memset ((void *) param, 0, sizeof (param)); /* zero the structures */
/* set up INT parameter */
param[0].buffer_type = MYSQL_TYPE_LONG;
param[0].buffer = (void *) &my_int;
param[0].is_unsigned = 0;
param[0].is_null = &is_null[0];
/* set up FLOAT parameter */
param[1].buffer_type = MYSQL_TYPE_FLOAT;
param[1].buffer = (void *) &my_float;
param[1].buffer = (void *) &my_float;
param[1].is_null = &is_null[1];
/* set up DATETIME parameter */
param[2].buffer_type = MYSQL_TYPE_DATETIME;
param[2].buffer = (void *) &my_datetime;
param[2].is_null = &is_null[2];
if (mysql_stmt_bind_result (stmt, param) != 0){
print_stmt_error (stmt, "Could not bind parameters for SELECT");
return;}
if (mysql_stmt_execute (stmt) != 0){
print_stmt_error (stmt, "Could not execute SELECT");
return;}
if (mysql_stmt_store_result (stmt) != 0){
print_stmt_error (stmt, "Could not buffer result set");
return;}
else{
printf ("Number of rows retrieved: %lu\n",
(unsigned long) mysql_stmt_num_rows (stmt));}
int ii = mysql_stmt_fetch (stmt);
while (ii == 0 || ii==MYSQL_DATA_TRUNCATED) /* fetch each row */
{
/* display row values */
printf ("%d ", my_int);
printf ("%.2f ", my_float);
printf ("%04d-%02d-%02d %02d:%02d:%02d\n",
my_datetime.year,
my_datetime.month,
my_datetime.day,
my_datetime.hour,
my_datetime.minute,
my_datetime.second);
ii=mysql_stmt_fetch (stmt);
}
mysql_stmt_free_result (stmt); /* deallocate result set */
}
