DDL with MariaDB Connector/C

MariaDB Connector/C supports DDL operations such as CREATE TABLE, ALTER TABLE, and TRUNCATE TABLE, letting C applications modify database schema by executing SQL statements with mysql_query().

C and C++ developers can use MariaDB Connector/C to perform basic DDL (Data Definition Language) operations with MariaDB database products.

DDL Operations

DDL (Data Definition Language) refers to all SQL-schema statements in the SQL standard (ISO/IEC 9075-2:2016).

Some examples of DDL include ALTER TABLE, CREATE TABLE, DROP TABLE, CREATE DATABASE, and TRUNCATE TABLE.

In MariaDB Connector/C, DDL statements are executed with mysql_query() (or mysql_real_query() for statements that contain binary data or null bytes).

Code Example: ALTER TABLE

ALTER TABLE is a DDL operation that changes an existing table.

The following code demonstrates how to execute ALTER TABLE on the example table:

#include <stdio.h>
#include <stdlib.h>
#include <mysql.h>

int main(int argc, char *argv[])
{
   // Initialize Connection
   MYSQL *conn;
   if (!(conn = mysql_init(0)))
   {
      fprintf(stderr, "unable to initialize connection struct\n");
      exit(1);
   }

   // Connect to the database
   if (!mysql_real_connect(
         conn,                  // Connection
         "mariadb.example.net", // Host
         "db_user",             // User account
         "db_user_password",    // User password
         "test",                // Default database
         3306,                  // Port number
         NULL,                  // Path to socket file
         0                      // Additional options
      ))
   {
      fprintf(stderr, "Error connecting to Server: %s\n", mysql_error(conn));
      mysql_close(conn);
      exit(1);
   }

   // Execute the ALTER TABLE statement
   if (mysql_query(conn, "ALTER TABLE test.contacts RENAME COLUMN first_name TO f_name"))
   {
      fprintf(stderr, "Error altering table: %s\n", mysql_error(conn));
      mysql_close(conn);
      exit(1);
   }

   // Close the Connection
   mysql_close(conn);

   return 0;
}

Confirm the table was altered by using MariaDB Client to execute a DESCRIBE statement on the same table:

DESC contacts;

+-----------+--------------+------+-----+---------+----------------+
| Field     | Type         | Null | Key | Default | Extra          |
+-----------+--------------+------+-----+---------+----------------+
| id        | int(11)      | NO   | PRI | NULL    | auto_increment |
| f_name    | varchar(25)  | YES  |     | NULL    |                |
| last_name | varchar(25)  | YES  |     | NULL    |                |
| email     | varchar(100) | YES  |     | NULL    |                |
+-----------+--------------+------+-----+---------+----------------+

Code Example: TRUNCATE TABLE

TRUNCATE TABLE is a DDL operation that deletes all data from an existing table.

To truncate the table instead, replace the ALTER TABLE statement in the code example above with:

   if (mysql_query(conn, "TRUNCATE test.contacts"))
   {
      fprintf(stderr, "Error truncating table: %s\n", mysql_error(conn));
      mysql_close(conn);
      exit(1);
   }

The following query confirms that TRUNCATE TABLE deleted all rows from the example table:

SELECT * FROM test.contacts;

Empty set (0.000 sec)

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