Check whether a sqlite3 table column is filled or not

Question

Requirement :

• Check whether a sqlite3 table column is filled or not and if it is not filled, fill up with a value.

• I assume that if data is not filled to a field that field will show as NULL.

Following commands I have tried, but the commands are not working for me.

UPDATE SET = 1 WHERE = NULL --> Not working

UPDATE SET = 1 WHERE IS NULL --> Not working

UPDATE SET = 1 WHERE = 0 --> Not working

UPDATE SET = 1 WHERE = '' --> Not working

Below is the c code I am using :

#include <stdio.h> /* needed for vsnprintf */
#include <stdarg.h> /* needed for va_list */
#include <stdlib.h> /* needed for malloc-free */
#include <string.h>
#include <sqlite3.h>


int main(int argc, char* argv[]) 
{
    sqlite3 *db;
    sqlite3_stmt *stmt;
    char *query = NULL, *zErrMsg = 0, *sql = NULL;
    char name[20] = "SAM";
    int rc, i = 100;


    /* Open database */
    rc = sqlite3_open("test.db", &db);
    if (rc) {
        fprintf(stderr, "Can't open database: %s\n", sqlite3_errmsg(db));
        while (1);
        return(0);
    }
    else {
        fprintf(stderr, "Opened database successfully..NEW\n");
    }

    /* Create a table */
    rc = sqlite3_exec(db, "create table demo (name text, age integer);", NULL, NULL, &zErrMsg);
    if (rc != SQLITE_OK)
    {
        printf("Error: %s:Unable to create the table\n", zErrMsg);
        while (1);
    }    

    asprintf(&query, "insert into demo (name) values ('%s');", name);
    /* Insert into table */
    sqlite3_prepare_v2(db, query, strlen(query), &stmt, NULL);                              /* 2 */ 
    if (sqlite3_step(stmt) == SQLITE_ROW)
    {
        printf("Inserted successfully\n");
    }
    if(stmt)
    {
        sqlite3_finalize(stmt);
        stmt = NULL;
    }   

    if(query)
    {
        free(query);
        query = NULL;   
    }

    asprintf(&query, "insert into demo (name, age) values ('%s',%d);", name, i);
    /* Insert into table */
    sqlite3_prepare_v2(db, query, strlen(query), &stmt, NULL);                              /* 2 */ 
    if (sqlite3_step(stmt) == SQLITE_ROW)
    {
        printf("Inserted successfully\n");
    }
    if(stmt)
    {
        sqlite3_finalize(stmt);
        stmt = NULL;
    }   

    if(query)
    {
        free(query);
        query = NULL;   
    }

    asprintf(&query, "insert into demo (name) values ('%s');", name);
    /* Insert into table */
    sqlite3_prepare_v2(db, query, strlen(query), &stmt, NULL);                              /* 3 */ 
    if (sqlite3_step(stmt) == SQLITE_ROW)
    {
        printf("Inserted successfully\n");
    }
    if(stmt)
    {
        sqlite3_finalize(stmt);
        stmt = NULL;
    }   

    if(query)
    {
        free(query);
        query = NULL;   
    }

    asprintf(&query, "UPDATE demo SET age = 1 WHERE age = NULL");
    stmt = NULL;
    rc = sqlite3_prepare_v2(db, query, -1, &stmt, 0);
    if (rc == SQLITE_OK)
    {
        printf("sqlite3_prepare_v2:Executed successfully\n");
    }   
    rc = sqlite3_step(stmt);                                                                    /* 3 */
    if (rc != SQLITE_DONE)
    {
        printf("ERROR inserting data: %s\n", sqlite3_errmsg(db));   
    }

    if(stmt)
    {
        sqlite3_finalize(stmt);
        stmt = NULL;
    }   

    if(query)
    {
        free(query);
        query = NULL;   
    }   
    sqlite3_close(db);      
    return 0;
}

Thanks in advance