Why Android Developers Must Learn SQL in 2026

import androidx.room.Entity
import androidx.room.PrimaryKey

@Entity(tableName = "notes")
data class Note(
    @PrimaryKey(autoGenerate = true) val id: Long = 0,
    val title: String,
    val body: String,
    val updatedAt: Long
)

CREATE TABLE notes (
    id         INTEGER PRIMARY KEY AUTOINCREMENT,
    title      TEXT NOT NULL,
    body       TEXT NOT NULL,
    updatedAt  INTEGER NOT NULL
);

import androidx.room.*
import kotlinx.coroutines.flow.Flow

@Dao
interface NoteDao {
    @Query("SELECT * FROM notes ORDER BY updatedAt DESC")
    fun observeAll(): Flow<List<Note>>

    @Query("SELECT * FROM notes WHERE title LIKE '%' || :q || '%'")
    fun search(q: String): Flow<List<Note>>

    @Query("SELECT COUNT(*) FROM notes")
    suspend fun count(): Int

    @Upsert
    suspend fun save(note: Note)
}

-- Notes with their folder name
SELECT n.id, n.title, f.name AS folder
FROM notes AS n
JOIN folders AS f ON f.id = n.folderId
WHERE f.name = 'Work'
ORDER BY n.updatedAt DESC;

@Entity(
    tableName = "notes",
    indices = [Index(value = ["updatedAt"])]
)
data class Note(
    @PrimaryKey(autoGenerate = true) val id: Long = 0,
    val title: String,
    val body: String,
    val updatedAt: Long
)

-- Run in Android Studio's Database Inspector
EXPLAIN QUERY PLAN
SELECT * FROM notes ORDER BY updatedAt DESC;
-- Look for 'USING INDEX' rather than a full 'SCAN'

CREATE TABLE folders (
    id   INTEGER PRIMARY KEY AUTOINCREMENT,
    name TEXT NOT NULL UNIQUE
);

CREATE TABLE notes (
    id        INTEGER PRIMARY KEY AUTOINCREMENT,
    folderId  INTEGER NOT NULL REFERENCES folders(id) ON DELETE CASCADE,
    title     TEXT NOT NULL,
    body      TEXT NOT NULL,
    updatedAt INTEGER NOT NULL
);
CREATE INDEX idx_notes_folder ON notes(folderId);

-- 1. Count notes in each folder
SELECT f.name, COUNT(n.id) AS total
FROM folders f LEFT JOIN notes n ON n.folderId = f.id
GROUP BY f.id;

-- 2. Five most recently edited notes
SELECT title FROM notes ORDER BY updatedAt DESC LIMIT 5;

-- 3. Delete empty folders
DELETE FROM folders
WHERE id NOT IN (SELECT DISTINCT folderId FROM notes);

Saturday
- Create entities, DAO and database class
- Insert sample data and list it in a screen
- Add search with LIKE
Sunday
- Add folders and a JOIN query
- Add an index and check EXPLAIN QUERY PLAN
- Write a migration that adds a 'pinned' column