The MySQL Server has a quite simple interface for plugins to create tables inside INFORMATION_SCHEMA. A minimal plugin for creating a table with nothing but a counter might look like this:
static int counter_fill_table(THD *thd, TABLE_LIST *tables, Item *cond)
{
ulonglong value= 0;
while (1)
{
table->field[0]->store(value++, true);
}
return 0;
}
static ST_FIELD_INFO counter_table_fields[]=
{
{"COUNT", 20, MYSQL_TYPE_LONGLONG, 0, MY_I_S_UNSIGNED, 0, 0},
{0, 0, MYSQL_TYPE_NULL, 0, 0, 0, 0}
};
static int counter_table_init(void *ptr)
{
ST_SCHEMA_TABLE *schema_table= (ST_SCHEMA_TABLE*)ptr;
schema_table->fields_info= counter_table_fields;
schema_table->fill_table= counter_fill_table;
return 0;
}
static struct st_mysql_information_schema counter_table_info =
{ MYSQL_INFORMATION_SCHEMA_INTERFACE_VERSION };
mysql_declare_plugin(counter)
{
MYSQL_INFORMATION_SCHEMA_PLUGIN,
&counter_table_info, /* type-specific descriptor */
"COUNTER", /* plugin and table name */
"My Name", /* author */
"An I_S table with a counter",/* description */
PLUGIN_LICENSE_GPL, /* license type */
counter_table_init, /* init function */
NULL, /* deinit function */
0x10, /* version */
NULL, /* no status variables */
NULL, /* no system variables */
NULL, /* no reserved information */
0 /* no flags */
}
mysql_declare_plugin_end;
This is quite straight forward and documented inside the MySQL documentation. It also has an obvious issue: It will run forever (at least if we assume we don't run in an out of memory situation). Luckily we might have a user who foresees this issue and added a WHERE clause like here:
SELECT COUNT FROM INFORMATION_SCHEMA.COUNTER WHERE COUNT < 10
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