Laravel的Query Builder提供了一種無(wú)需編寫原生SQL即可構(gòu)建數(shù)據(jù)庫(kù)查詢的流暢方式，1. 使用DB門面可直接查詢表數(shù)據(jù)，如DB::table('users')->get()獲取所有用戶；2. 常用方法包括get()、first()、pluck()、take()進(jìn)行數(shù)據(jù)檢索，where()、orWhere()、whereIn()、whereNull()添加條件，orderBy()、latest()排序，join()關(guān)聯(lián)表，count()、max()等聚合函數(shù)；3. 支持insert()插入數(shù)據(jù)，update()更新數(shù)據(jù)，delete()刪除數(shù)據(jù)，truncate()清空表；4. 高級(jí)用法包含DB::raw()執(zhí)行原生表達(dá)式，when()條件式查詢，子查詢嵌套；5. 可與Eloquent模型結(jié)合使用，如User::where()->get()返回模型實(shí)例；Query Builder適用於復(fù)雜查詢且性能優(yōu)於Eloquent，調(diào)試時(shí)可用toSql()查看SQL語(yǔ)句，最終實(shí)現(xiàn)簡(jiǎn)潔高效的數(shù)據(jù)庫(kù)操作。

Laravel's Query Builder is a powerful and fluent way to construct and run database queries without writing raw SQL. It's part of Laravel's Eloquent ORM but can be used independently with database tables. Here's how to use it effectively.

1. Using the DB Facade

To start using the Query Builder, import and use Laravel's DB facade:

 use Illuminate\Support\Facades\DB;

Then you can query any table like this:

 $users = DB::table('users')->get();

This retrieves all rows from the users table.

2. Common Query Builder Methods

Here are the most commonly used methods with examples:

? Retrieve Data

• Get all rows:

   $users = DB::table('users')->get();

• Get first row:

   $user = DB::table('users')->first();

• Get specific columns:

   $names = DB::table('users')->pluck('name');

• Limit results:

   $someUsers = DB::table('users')->take(5)->get();

? Add WHERE Clauses

• Simple where:

   $user = DB::table('users')->where('active', 1)->get();

• Chained conditions (AND):

   $user = DB::table('users')
      ->where('status', 'active')
      ->where('age', '>', 18)
      ->get();

• OR conditions:

   $user = DB::table('users')
      ->where('votes', '>', 100)
      ->orWhere('name', 'John')
      ->get();

• Where in:

   $users = DB::table('users')
      ->whereIn('id', [1, 2, 3])
      ->get();

• Null checks:

   $users = DB::table('users')
      ->whereNull('updated_at')
      ->get();

? Sorting & Ordering

 $users = DB::table('users')
    ->orderBy('name', 'desc')
    ->get();

You can also use latest() and oldest() for timestamp columns:

 $user = DB::table('users')->latest()->first();

? Joins

 $users = DB::table('users')
    ->join('contacts', 'users.id', '=', 'contacts.user_id')
    ->select('users.name', 'contacts.phone')
    ->get();

Supports leftJoin , rightJoin , etc.

? Aggregates

 $count = DB::table('users')->count();
$max = DB::table('orders')->max('price');
$avg = DB::table('orders')->avg('price');

3. Insert, Update, Delete

? Insert Data

 DB::table('users')->insert([
    'name' => 'John Doe',
    'email' => 'john@example.com',
    'created_at' => now(),
    'updated_at' => now(),
]);

For getting the inserted ID (if the table has an auto-incrementing ID):

 $id = DB::table('users')->insertGetId([
    'name' => 'Jane Doe',
    'email' => 'jane@example.com',
    'created_at' => now(),
    'updated_at' => now(),
]);

? Update Data

 $affected = DB::table('users')
    ->where('id', 1)
    ->update([
        'email' => 'newemail@example.com',
        'updated_at' => now(),
    ]);

Returns the number of affected rows.

? Delete Data

 $deleted = DB::table('users')
    ->where('id', 1)
    ->delete();

Or delete all:

 DB::table('users')->truncate(); // Removes all rows

4. Advanced Usage

? Raw Expressions

Use DB::raw() to inject raw SQL:

 $users = DB::table('users')
    ->select(DB::raw('count(*) as user_count, status'))
    ->where(&#39;status&#39;, &#39;<>&#39;, 1)
    ->groupBy(&#39;status&#39;)
    ->get();

Be cautious with raw expressions to avoid SQL injection.

? Conditional Clauses

Use when() to apply conditions only when needed:

 $role = 'admin';
$users = DB::table('users')
    ->when($role, function ($query, $role) {
        return $query->where('role', $role);
    })
    ->get();

This only applies the where clause if $role is truthy.

? Subqueries (Laravel 6 )

 $latestLogin = DB::table('logins')
    ->select('user_id')
    ->whereColumn('user_id', 'users.id')
    ->orderBy('login_at', 'desc')
    ->limit(1);

$users = DB::table('users')
    ->select('users.*')
    ->where('id', 'in', $latestLogin)
    ->get();

5. Using with Models (Eloquent)

Even though Eloquent models use the Query Builder under the hood, you can still use it directly on models:

 $users = User::where('active', 1)->orderBy('name')->get();

This returns Eloquent models, not plain objects.

Final Notes

• The Query Builder is great for complex queries or when you don't need full Eloquent features.
• It's faster than Eloquent for simple operations because it doesn't instantiate model objects.
• Always sanitize input when using raw expressions.
• Use dd() or toSql() dd() for debugging:

 $query = DB::table('users')->where('active', 1);
echo $query->toSql(); // SELECT * FROM users WHERE active = ?

Basically, the Query Builder gives you a clean, expressive way to interact with your database — no raw SQL needed in most cases.

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