General error: 1215 Cannot add foreign key constraint

Your column types in both tables need to be identical, including any indexes. Try adding $table->index('a_id'); or I think you can chain ->index()to your unsignedintegers before you create your foreign key (repeat for the other migrations)

@D9705996 - That doesn't solve the problem

Just noticed that you have recursive foreign keys which is probably the main issue. You might need a third migration just to apply the foreign key constraints as it will ensure both tables exist. Also do you really want the alumni to be deleted when you delete the student?

Yas... its required .... I'll trying creating another migration

Whichever migration you run first, the other table will not exist. Create a seperate migration or run all three together. There is nothing stopping you from migrating all in one file;

 public function up()
{
    Schema::create('alumni', function (Blueprint $table) {
        $table->increments('aid');
        $table->integer('slot_id');
        $table->time('s_time');
        $table->time('e_time');
        $table->boolean('is_booked');
        $table->unsignedInteger('s_id');
        $table->timestamps();
    });

    Schema::create('students', function (Blueprint $table) {
        $table->increments('sid');
        $table->unsignedInteger('a_id');
        $table->time('slot');
        $table->timestamp('date');
        $table->boolean('status');
        $table->timestamps();
    });

    Schema::table('students', function (Blueprint $table) {
        $table->foreign('a_id')->references('aid')->on('alumni')->onDelete('cascade');
    }

    Schema::table('alumni', function (Blueprint $table) {
        $table->foreign('s_id')->references('sid')->on('students')->onDelete('cascade');
    }


}

}

@D9705996 - Thanks another migration worked

@MIKE_3096 - Glad you got it sorted. Could you please mark the discussion as solved

@D9705996 - Sure... there is one more thing i'm stuck with how can i enter data in such table as either of the table cannot be filled due to recursive foreign key because they contain their respective primary keys in each other..

@MIKE_3096 - That's a bigger question as to me your data model sounds wrong. You currently have a one to one relationship between student and alumni.

It sounds like you actually have a many to many e.g. a student is a member of an alumni and alumni has many students..

You need a many to many relationship which would sort your issue

https://laravel.com/docs/5.7/eloquent-relationships#many-to-many

@D9705996 - ya actually ....... just went the documentation ...... finally sorted things.... Thanks again

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