Mysql Patterns

MySQL Patterns

Use this skill when working on MySQL or MariaDB schema design, migrations, slow-query investigation, queue-style transactions, connection pools, or production database configuration. Prefer exact version checks before applying a feature-specific pattern because MySQL and MariaDB have diverged in several SQL details.

Activation

• Designing MySQL or MariaDB tables, indexes, and constraints
• Reviewing migrations before they run on large production tables
• Debugging slow queries, lock waits, deadlocks, or connection exhaustion
• Adding keyset pagination, upserts, full-text search, JSON columns, or queues
• Configuring application connection pools, read replicas, TLS, or slow logs

Version Check

Start by identifying the engine and version:

SELECT VERSION();
SHOW VARIABLES LIKE 'version_comment';

Keep MySQL and MariaDB guidance separate when syntax differs:

• MySQL documents row aliases as the replacement for VALUES(col) in ON DUPLICATE KEY UPDATE; VALUES(col) is deprecated there.
• MariaDB documents VALUES(col) as the supported way to reference inserted values in ON DUPLICATE KEY UPDATE; use it for cross-engine compatibility.
• SKIP LOCKED is appropriate for queue-like work only. It skips locked rows and can return an inconsistent view, so do not use it for general accounting or integrity-sensitive reads.

Schema Defaults

CREATE TABLE orders (
    id BIGINT UNSIGNED NOT NULL AUTO_INCREMENT,
    account_id BIGINT UNSIGNED NOT NULL,
    status VARCHAR(32) NOT NULL,
    total DECIMAL(15, 2) NOT NULL,
    created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
    updated_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
    deleted_at DATETIME NULL,
    PRIMARY KEY (id),
    KEY idx_orders_account_status_created (account_id, status, created_at),
    KEY idx_orders_active (account_id, deleted_at)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

Default choices:

Indexing

Composite index order usually follows equality predicates first, then range or sort columns:

CREATE INDEX idx_orders_account_status_created
    ON orders (account_id, status, created_at);

SELECT id, total
FROM orders
WHERE account_id = ?
  AND status = 'pending'
  AND created_at >= ?
ORDER BY created_at DESC
LIMIT 50;

Use EXPLAIN before adding or changing an index:

EXPLAIN
SELECT id, total
FROM orders
WHERE account_id = 123 AND status = 'pending'
ORDER BY created_at DESC
LIMIT 50;

Signals to investigate:

Avoid adding indexes blindly. Each index increases write cost, migration time, backup size, and buffer-pool pressure.

Query Patterns

Upsert

Cross-engine-compatible form:

INSERT INTO user_settings (user_id, setting_key, setting_value)
VALUES (?, ?, ?)
ON DUPLICATE KEY UPDATE
    setting_value = VALUES(setting_value),
    updated_at = CURRENT_TIMESTAMP;

MySQL row-alias form:

INSERT INTO user_settings (user_id, setting_key, setting_value)
VALUES (?, ?, ?) AS new
ON DUPLICATE KEY UPDATE
    setting_value = new.setting_value,
    updated_at = CURRENT_TIMESTAMP;

Use the row-alias form only after confirming the target is MySQL. Use VALUES(col) for MariaDB or mixed MySQL/MariaDB fleets.

Keyset Pagination

SELECT id, name, created_at
FROM products
WHERE (created_at, id) < (?, ?)
ORDER BY created_at DESC, id DESC
LIMIT 50;

Back it with an index that matches the cursor:

CREATE INDEX idx_products_created_id ON products (created_at, id);

Do not use deep OFFSET pagination on large tables; it makes the server scan and discard rows before returning the page.

JSON Fields

Use JSON columns for extension data, not for fields that need heavy relational filtering or constraints.

CREATE TABLE events (
    id BIGINT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
    payload JSON NOT NULL,
    event_type VARCHAR(64)
        GENERATED ALWAYS AS (JSON_UNQUOTE(JSON_EXTRACT(payload, '$.type'))) STORED,
    KEY idx_events_type (event_type)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;

For frequently queried JSON paths, expose a generated column and index that column. Keep foreign keys, ownership, tenancy, and lifecycle fields relational.

Full-Text Search

ALTER TABLE articles ADD FULLTEXT KEY ft_articles_title_body (title, body);

SELECT id, title, MATCH(title, body) AGAINST (? IN NATURAL LANGUAGE MODE) AS score
FROM articles
WHERE MATCH(title, body) AGAINST (? IN NATURAL LANGUAGE MODE)
ORDER BY score DESC
LIMIT 20;

Use external search when you need typo tolerance, complex ranking, cross-table facets, or language-specific analysis beyond built-in full-text behavior.

Transactions

Keep transactions short and lock rows in a consistent order:

START TRANSACTION;

SELECT id, balance
FROM accounts
WHERE id IN (?, ?)
ORDER BY id
FOR UPDATE;

UPDATE accounts SET balance = balance - ? WHERE id = ?;
UPDATE accounts SET balance = balance + ? WHERE id = ?;

COMMIT;

Deadlock and lock-wait checklist:

• Lock rows in a deterministic order across code paths.
• Do external API calls before opening the transaction, not inside it.
• Add indexes for predicates used in UPDATE, DELETE, and locking reads.
• On deadlock, roll back and retry the whole transaction with a bounded retry budget.
• Capture SHOW ENGINE INNODB STATUS\G soon after a deadlock; it is overwritten by later events.

Queue-style worker claim:

START TRANSACTION;

SELECT id
FROM jobs
WHERE status = 'pending'
ORDER BY created_at
LIMIT 1
FOR UPDATE SKIP LOCKED;

UPDATE jobs
SET status = 'processing', started_at = CURRENT_TIMESTAMP
WHERE id = ?;

COMMIT;

Use SKIP LOCKED only for queue-like workloads where skipping a locked row is acceptable. It is not a replacement for normal transactional consistency.