Database terms
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Most referenced — Database
INSERT ... ON DUPLICATE KEY UPDATE 2N+1 Query Problem 2JSON Columns in MySQL & PostgreSQL 1Database Triggers 1Transaction Isolation Levels 1Database Deadlocks 1Query Optimisation 1Database Indexes 1
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Common Table Expressions (CTEs)
PHP 5.0+
1
Named temporary result sets defined with the WITH clause that can be referenced in a query, improving readability and enabling recursive queries.
3mo ago
Database intermediate
Composite Index Design
PHP 5.0+
1
A composite index covers multiple columns — column order determines which queries benefit, following the leftmost prefix rule.
3mo ago
Database advanced
Database Deadlocks
PHP 5.0+
1
A situation where two or more transactions hold locks the other needs, each waiting indefinitely — resolved by the database killing one transaction.
3mo ago
Database advanced
Database Indexes — Types & Trade-offs
PHP 5.0+ B-Tree, hash, full-text, and partial indexes — each suited to different query patterns, with write overhead as the cost of read speed.
3mo ago
Database intermediate
Database Normalisation
1
The process of structuring a relational database to reduce redundancy and improve integrity, defined through progressive normal forms (1NF through BCNF).
3mo ago
Database intermediate
Database Schema Design
PHP 5.0+
5
The process of defining tables, columns, data types, constraints, and relationships — decisions made at schema design time are expensive to reverse once data is live.
3mo ago
Database intermediate
Database Transactions
PHP 5.1+ A sequence of SQL operations treated as a single atomic unit — all succeed or all roll back — enforcing ACID guarantees.
3mo ago
Database intermediate
Database Views & Materialised Views
PHP 5.0+
1
A view is a saved SELECT query presented as a virtual table. A materialised view stores the query result physically — trading freshness for query speed.
3mo ago
Database intermediate
EXPLAIN & Query Plans
PHP 5.0+
EXPLAIN (ANALYZE) reveals how the database executes a query — sequential scans, index scans, join strategies — to guide optimisation.
3mo ago
Database intermediate
EXPLAIN ANALYZE
PHP 5.0+ The database command that shows the actual execution plan of a query — revealing sequential scans, missing indexes, and row estimate errors that cause slow performance.
3mo ago
Database advanced
Foreign Keys & Referential Integrity
PHP 5.0+
1
A foreign key is a column that references the primary key of another table, enforcing referential integrity — no orphaned rows pointing to non-existent parents.
3mo ago
Database intermediate
JSON Columns in MySQL & PostgreSQL
PHP 5.0+ Native JSON column types allow storing and querying semi-structured data within a relational database — without sacrificing ACID guarantees or the ability to index specific JSON paths.
3mo ago
Database intermediate
Keyset Pagination
PHP 5.0+ A pagination technique using WHERE id > :last_seen_id instead of OFFSET, providing consistent O(log n) performance regardless of page depth.
3mo ago
Database intermediate
N+1 Queries — Detection & Fix
PHP 5.0+ Issuing one query per row of a result set instead of a single JOIN — the most common database performance mistake in any ORM-based application.
3mo ago
Database intermediate
Pessimistic vs Optimistic Locking
PHP 5.0+ Pessimistic locking acquires a database lock upfront preventing conflicts. Optimistic locking detects conflicts at write time using a version column — trading lock overhead for conflict detection.
3mo ago
Database advanced
Safe Database Migration Patterns
PHP 5.0+ Expand-contract, backward-compatible migrations run alongside a zero-downtime deploy — never rename or drop columns in the same deploy as the code change.
3mo ago
Database intermediate
SQL Window Functions
PHP 5.0+
SQL functions that perform calculations across a set of rows related to the current row without collapsing them into a single output row.
3mo ago
Database advanced
Stored Procedures vs Application Logic
PHP 5.0+
Stored procedures execute business logic inside the database — close to data but hard to test, version, and deploy. Application logic is more maintainable but requires more round-trips.
3mo ago
Database intermediate
Transaction Isolation Levels
PHP 5.1+ SQL standards defining how and when changes made by one transaction are visible to others, trading consistency for concurrency.
3mo ago
Database advanced
UPSERT
PHP 5.0+
An atomic INSERT-or-UPDATE operation — inserts the row if it does not exist, updates it if it does — eliminating the race condition of a separate check-then-insert.
3mo ago
Database intermediate