Apa iku SQL lan apa gunane?

Question

Accepted Answer

**SQL** (Structured Query Language) yaiku basa standar kanggo nggarap **database relasional** — nyimpen, nanyuk, lan ngatur data sing disusun dadi **tabel** (baris lan kolom). Iku *deklaratif*: sampeyan jelasake *apa* data sing sampeyan pengin, lan engine database ngerti *carane* ngambil luwih efisien.

## Query prasaja

```sql
SELECT name, email          -- WHAT columns you want
FROM users                  -- from which table
WHERE active = true         -- filter rows
ORDER BY name;              -- sort the result
```

Sampeyan nyatakake asil sing dikarepake; query planner database mutusakne strategi eksekusi (indeks apa sing bakal dienggo, carane join, lsp.).

## Kategori perintah SQL

```text
DQL  (Data Query)       → SELECT — read data (the most-used)
DML  (Data Manipulation)→ INSERT, UPDATE, DELETE — change rows
DDL  (Data Definition)  → CREATE, ALTER, DROP — define/change schema (tables, indexes)
DCL  (Data Control)     → GRANT, REVOKE — permissions
TCL  (Transaction)      → COMMIT, ROLLBACK — transaction control
```

## Model relasional

```text
Data lives in TABLES (relations): rows (records) × columns (fields).
Tables relate via KEYS (primary key identifies a row; foreign key references another table).
→ SQL queries combine and filter this structured, related data.
```

## Standar, kanthi dialek

```text
SQL is an ANSI/ISO standard, but each database has its own DIALECT:
  PostgreSQL, MySQL, SQL Server, Oracle, SQLite — mostly compatible, with extras.
→ Core SQL transfers across databases; specific features/functions vary.
```

## Ora apa pentinge

SQL minangka salah sawijining teknologi paling penting lan tahan lama ing software — database relasional nyukupi mayoritas aplikasi, lan SQL yaiku basa universal kanggo nggarap, mula ngerte iku penting kanggo nyambut gawé back-end utawa data.

Sifate **deklaratif** (jelasake *apa* sing pengin, ora *carane* ngambil) yaiku konsep utama: sampeyan nulis query lan engine database ngoptimalkake eksekusi, iku kuat nanging uga guna ngapa ngerte indexing lan query optimization iku penting (pilihan engine ngaruhi performa).

Ngerte kategori perintah (DQL/DML/DDL/DCL/TCL — khususé SELECT kanggo maca lan INSERT/UPDATE/DELETE kanggo ngganti data), model relasional (tabel, baris, kolom, kunci), lan SQL yaiku standar kanthi dialek spesifik database ngabdi kabeh babagan nggarap database.

Amarga persistensi data penting kanggo akeh aplikasi lan SQL yaiku interface standar kanggo data relasional (digawe dening developer, data analyst, lan akeh peran), SQL yaiku ngelmu dasar lan kudu diweruhi — wis penting kanggo puluhan taun lan tetep kaya mangkono, dadi salah sawijining skill paling berharga ing pengembangan software.