SQLShack
SQLShack
Free article library started by ApexSQL, written by SQL Server professionals, covering T-SQL, indexing, query tuning, backup and recovery, high availability, auditing and SSIS. Readers can follow step-by-step examples to administer, secure and tune SQL Server instances.
More resources on Database Administration
use-the-index-luke.com
A practical guide to database indexing and query optimization, offering clear explanations of how indexes work, how to design them, and tutorials with SQL examples across major relational databases.
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Four-hour freeCodeCamp course walking through PostgreSQL from installation and psql basics to table design, constraints, joins, aggregate functions, exporting data and UUID keys. Viewers finish able to set up a database and run realistic queries against it.
DBA Stack Exchange
Stack Exchange site where working database administrators answer questions on query tuning, replication, backups, indexing and upgrades across MySQL, PostgreSQL, SQL Server and Oracle. Voting surfaces tested answers, and searching past threads usually resolves operational problems quickly.
Percona Blog
Engineering blog from Percona, a MySQL, PostgreSQL and MongoDB support vendor. Posts benchmark storage engines, dissect replication and failover behaviour, and explain version changes, giving practitioners evidence-based guidance on tuning and operating open-source databases in production.
Database Administration: The Complete Guide
Craig Mullins covers the DBA role end to end: data modelling, schema design, change management, backup and recovery, performance monitoring, security and disaster planning. Written to be DBMS-independent, so the practices carry across Oracle, DB2 and SQL Server.
dba-oracle.com
DBA-Oracle is a resource focused on Oracle database administration, offering tutorials, guides, and practical tips for DBAs. Content covers SQL/PLSQL, performance tuning, backup and recovery (RMAN), high availability (RAC/Data Guard), security, and other DBA best practices.