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DBMS → Introduction to DBMS 17

To attach tags to a question in Eloquent M:N
$question->tags()->attach($tagIds)
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To remove all tag associations from a question in Eloquent M:N
$question->tags()->detach()
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$question->tags()->sync($newTagIds) in Eloquent
Adds new tags and removes old ones so the relationship matches exactly $newTagIds
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Which Eloquent method creates a model AND saves it to database in one step
Question::create(['question'=>'...'])
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Question::firstOrCreate(['question'=>'Test?'],['option_a'=>'A']) does
Finds first matching row or creates it if not found
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Question::updateOrCreate(['id'=>1],['q_level'=>3]) does
Updates if found by first arg, creates if not found
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Which prevents concurrent duplicate inserts in Laravel
Unique database constraint + try-catch for IntegrityConstraintViolationException
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Database connection pooling improves
Performance by reusing existing connections instead of creating new ones for each request
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Which Laravel config file sets database connection settings
config/database.php (reads from .env variables)
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DB_CONNECTION=mysql in .env sets
The database driver (mysql, pgsql, sqlite, sqlsrv)
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To add a new column 'marks' INT DEFAULT 0 to existing questions table in Laravel migration
Schema::table('questions', function(Blueprint $t){ $t->integer('marks')->default(0); })
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$table->after('solution') in migration column definition
Places the new column AFTER the solution column in the table structure
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$table->change() in migration is used to
Rename table
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Which SQL command shows FK constraints on questions table in MySQL
SELECT * FROM information_schema.KEY_COLUMN_USAGE WHERE TABLE_NAME='questions'
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To safely drop a column that might not exist in migration
Schema::table('questions',fn($t)=>$t->dropColumn('old_col')) in a try-catch or use Schema::hasColumn() check first
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Which is the correct way to handle database errors in Laravel
Catch Illuminate\\Database\\QueryException for DB errors
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Which PHP/Laravel code correctly inserts a question matching the screenshot table format
Both A and C are correct
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DBMS → SQL Basics 1

Which SQL query most efficiently counts questions per q_level without NULL q_level
SELECT q_level,COUNT(*) FROM questions WHERE q_level IS NOT NULL GROUP BY q_level
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DBMS → Relational Model 1

To add a foreign key constraint to existing questions.assignment_id column in migration
$table->foreign('assignment_id')->references('id')->on('assignments')->onDelete('cascade')
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DBMS → Transactions 3

DB::transaction(function(){ /* multiple inserts */ }) advantage
Ensures all inserts succeed or all fail atomically - no partial data
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DB::table('questions')->lockForUpdate() in a transaction
Acquires an exclusive lock preventing other transactions from reading/writing these rows
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DB::table('questions')->sharedLock() in a transaction
Acquires a shared lock allowing reads but preventing exclusive locks from other transactions
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