db_query

// entity_storage.inc

EntityStorage_SpawnAll(DB:connectionHandle)
{
    // Select all entries in table "entities"
    new DBResult:db_result_set = db_query(connectionHandle, "SELECT * FROM `entities`");

    // If database result set handle is valid
    if (db_result_set)
    {
        // Do something...

        // Free the result set
        db_free_result(db_result_set);
    }
}

// mode.pwn

#include <entity_storage>

static DB:gDBConnectionHandle;

// ...

public OnGameModeInit()
{
    // ...

    // Create a connection to a database
    gDBConnectionHandle = db_open("example.db");

    // If connection to the database exists
    if (gDBConnectionHandle)
    {
        // Successfully created a connection to the database
        print("Successfully created a connection to database \"example.db\".");
        EntityStorage_SpawnAll(gDBConnectionHandle);
    }
    else
    {
        // Failed to create a connection to the database
        print("Failed to open a connection to database \"example.db\".");
    }

    // ...

    return 1;
}

public OnGameModeExit()
{
    // Close the connection to the database if connection is open
    if (db_close(gDBConnectionHandle))
    {
        // Extra cleanup
        gDBConnectionHandle = DB:0;
    }

    // ...

    return 1;
}