mysql:sql:dml

• What it is: DML (Data Manipulation Language) is the set of SQL statements used to read and modify table data.
• What it’s for: Do CRUD operations: create rows, read rows, update rows, delete rows.
• Core keywords:
  • SELECT /sɪˈlekt/ — select (chọn / truy vấn)
  • INSERT /ɪnˈsɝːt/ — insert (chèn)
  • UPDATE /ʌpˈdeɪt/ — update (cập nhật)
  • DELETE /dɪˈliːt/ — delete (xóa)

• Example (create a table to practice):

CREATE TABLE users (
  id BIGINT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
  email VARCHAR(255) NOT NULL,
  name VARCHAR(100) NULL,
  created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
  UNIQUE KEY uk_users_email (email)
);

• Example (INSERT):

INSERT INTO users (email, name) VALUES ('a@b.com', 'Alice');
INSERT INTO users (email) VALUES ('c@d.com'); -- name is NULL

• Example (SELECT basics):

SELECT id, email, name FROM users;
SELECT * FROM users WHERE email = 'a@b.com';
SELECT * FROM users ORDER BY id DESC LIMIT 10;

• Example (WHERE operators):

SELECT * FROM users WHERE id = 1;
SELECT * FROM users WHERE id IN (1,2,3);
SELECT * FROM users WHERE email LIKE '%@b.com';
SELECT * FROM users WHERE created_at >= '2026-01-01';

• Example (UPDATE):

UPDATE users SET name = 'Alice Nguyen' WHERE email = 'a@b.com';
UPDATE users SET name = NULL WHERE id = 1;

• Example (DELETE):

DELETE FROM users WHERE id = 1;

• Safe habits (best practice):
  • Always add a WHERE clause for UPDATE/DELETE (unless you truly want to affect all rows).
  • Prefer LIMIT when testing deletes/updates in production-like environments.

• Vocabulary (hard words):
  • clause /klɔːz/ — clause (mệnh đề trong câu SQL, ví dụ WHERE clause)
  • affect /əˈfekt/ — affect (tác động)
  • production /prəˈdʌk.ʃən/ — production (môi trường thật)