Database systems workbook: foundations, the relational model, normalization, SQL, storage, indexing, and real DBMS engines.http://localhost:4321/http://localhost:4321/dbms/deduplication-pattern/http://localhost:4321/dbms/deduplication-pattern/ROW_NUMBER() OVER (PARTITION BY ...) = 1 and the DISTINCT ON (Postgres) alternatives for keeping one row per group.Sun, 31 May 2026 00:00:00 GMTFoundationalpatternSQL Patternssqlsql-patterndeduplicationwindow-functionsdistinct-onhttp://localhost:4321/dbms/existence-check-pattern/http://localhost:4321/dbms/existence-check-pattern/EXISTS vs NOT EXISTS vs IN vs LEFT JOIN IS NULL — four ways to say where this related row does or does not exist.Sun, 31 May 2026 00:00:00 GMTFoundationalpatternSQL Patternssqlsql-patternsubqueriesjoinsnullshttp://localhost:4321/dbms/gaps-and-islands-pattern/http://localhost:4321/dbms/gaps-and-islands-pattern/The streak-detection template: subtract row number from a value, group by the difference. Identifies runs of consecutive rows.Sun, 31 May 2026 00:00:00 GMTAdvancedpatternSQL Patternssqlsql-patternwindow-functionsstreakssequenceshttp://localhost:4321/dbms/group-bucket-pattern/http://localhost:4321/dbms/group-bucket-pattern/Bucket continuous values into ranges (age bands, price tiers) using CASE WHEN inside GROUP BY.Sun, 31 May 2026 00:00:00 GMTFoundationalpatternSQL Patternssqlsql-patternaggregationbucketingcase-whenhttp://localhost:4321/dbms/join-variants-pattern/http://localhost:4321/dbms/join-variants-pattern/Self-join, anti-join, semi-join, lateral join, theta-join. Beyond the standard four kinds of join.Sun, 31 May 2026 00:00:00 GMTIntermediatepatternSQL Patternssqlsql-patternjoinslateralanti-joinsemi-joinhttp://localhost:4321/dbms/lead-lag-navigation-pattern/http://localhost:4321/dbms/lead-lag-navigation-pattern/LEAD() and LAG() for previous/next-row comparison. Streak detection, change-from-previous metrics, run-length tracking.Sun, 31 May 2026 00:00:00 GMTIntermediatepatternSQL Patternssqlsql-patternwindow-functionsnavigationstreakshttp://localhost:4321/dbms/nested-query-pattern/http://localhost:4321/dbms/nested-query-pattern/Correlated vs uncorrelated subqueries; subquery in SELECT vs WHERE vs FROM. When CTEs beat nested subqueries.Sun, 31 May 2026 00:00:00 GMTIntermediatepatternSQL Patternssqlsql-patternsubqueriesctecorrelatedhttp://localhost:4321/dbms/patch-gaps-pattern/http://localhost:4321/dbms/patch-gaps-pattern/Fill missing rows in a sequence with default values via LEFT JOIN against a generated calendar or series.Sun, 31 May 2026 00:00:00 GMTIntermediatepatternSQL Patternssqlsql-patternjoinstime-seriescalendarhttp://localhost:4321/dbms/pattern-search-pattern/http://localhost:4321/dbms/pattern-search-pattern/LIKE, ILIKE, regex, trigram, full-text — the spectrum of find rows that match a string pattern.Sun, 31 May 2026 00:00:00 GMTFoundationalpatternSQL Patternssqlsql-patternsearchfull-textindexinghttp://localhost:4321/dbms/pivot-flip-pattern/http://localhost:4321/dbms/pivot-flip-pattern/Long-to-wide and wide-to-long reshapes. PIVOT (T-SQL), crosstab (Postgres), conditional aggregation as the portable form.Sun, 31 May 2026 00:00:00 GMTIntermediatepatternSQL Patternssqlsql-patternpivotreshapeaggregationhttp://localhost:4321/dbms/rank-and-row-pattern/http://localhost:4321/dbms/rank-and-row-pattern/ROW_NUMBER vs RANK vs DENSE_RANK. Per-partition top-N selection. The second-highest-salary canon.Sun, 31 May 2026 00:00:00 GMTIntermediatepatternSQL Patternssqlsql-patternwindow-functionsrankingtop-nhttp://localhost:4321/dbms/recursive-tree-pattern/http://localhost:4321/dbms/recursive-tree-pattern/Recursive CTEs (WITH RECURSIVE) for tree traversal, transitive closures, organisational hierarchies.Sun, 31 May 2026 00:00:00 GMTAdvancedpatternSQL Patternssqlsql-patternrecursive-ctehierarchiesgraphshttp://localhost:4321/dbms/rolling-totals-pattern/http://localhost:4321/dbms/rolling-totals-pattern/Cumulative aggregations over a window. SUM() OVER (ORDER BY ... ROWS BETWEEN ...). The time-series running-total template.Sun, 31 May 2026 00:00:00 GMTIntermediatepatternSQL Patternssqlsql-patternwindow-functionsaggregationtime-serieshttp://localhost:4321/dbms/set-compare-pattern/http://localhost:4321/dbms/set-compare-pattern/INTERSECT / EXCEPT / UNION and the equivalent JOIN / NOT EXISTS forms. When set algebra beats joins.Sun, 31 May 2026 00:00:00 GMTIntermediatepatternSQL Patternssqlsql-patternset-operationsunionintersectexcepthttp://localhost:4321/dbms/tally-count-pattern/http://localhost:4321/dbms/tally-count-pattern/Count occurrences of values in a column. The COUNT(*) GROUP BY template every SQL interview opens with.Sun, 31 May 2026 00:00:00 GMTFoundationalpatternSQL Patternssqlsql-patternaggregationgroup-bycounthttp://localhost:4321/dbms/aggregates-group-by-having/http://localhost:4321/dbms/aggregates-group-by-having/COUNT / SUM / AVG / MIN / MAX, the GROUP BY contract, why HAVING is not WHERE.Sun, 24 May 2026 00:00:00 GMTFoundationalbuilding-blockSQLaggregatesgroup-byhavingsqlanalyticshttp://localhost:4321/dbms/1nf-2nf-3nf/http://localhost:4321/dbms/1nf-2nf-3nf/Atomicity, full functional dependency, transitive dependency — the three levels every relational schema starts with.Sun, 24 May 2026 00:00:00 GMTIntermediateconceptNormalizationnormalization1nf2nf3nfhttp://localhost:4321/dbms/bcnf-and-beyond/http://localhost:4321/dbms/bcnf-and-beyond/BCNF as the strict-3NF; the pragmatic stopping point and where denormalization is genuinely worth it.Sun, 24 May 2026 00:00:00 GMTIntermediateconceptNormalizationnormalizationbcnf4nfdenormalizationhttp://localhost:4321/dbms/classification-of-dbms/http://localhost:4321/dbms/classification-of-dbms/Relational vs document vs key-value vs graph vs columnar vs time-series. What each is good at and where the boundaries blur.Sun, 24 May 2026 00:00:00 GMTFoundationalconceptFoundationsclassificationnosqloltpolapdata-modelshttp://localhost:4321/dbms/dbms-architecture-three-schemas/http://localhost:4321/dbms/dbms-architecture-three-schemas/Conceptual, logical, and physical schemas; data independence; how a schema change at one level shouldn't break the others.Sun, 24 May 2026 00:00:00 GMTFoundationalconceptFoundationsarchitectureschemasdata-independenceansi-sparchttp://localhost:4321/dbms/data-models-and-schemas/http://localhost:4321/dbms/data-models-and-schemas/Model = vocabulary. Schema = structure. Instance = data. The difference matters for migration, validation, and discussion.Sun, 24 May 2026 00:00:00 GMTFoundationalconceptData Modelingdata-modelschemainstancemodelinghttp://localhost:4321/dbms/ddl-create-alter-drop/http://localhost:4321/dbms/ddl-create-alter-drop/Defining the schema. Tables, columns, constraints, indexes — and the ALTER traps on a live system.Sun, 24 May 2026 00:00:00 GMTFoundationalbuilding-blockSQLddlschemaalter-tablemigrationsddl-lockshttp://localhost:4321/dbms/dml-insert-update-delete/http://localhost:4321/dbms/dml-insert-update-delete/Mutating data. RETURNING, UPSERT / ON CONFLICT, the things to know about row-locking on writes.Sun, 24 May 2026 00:00:00 GMTFoundationalbuilding-blockSQLdmlinsertupdatedeleteupserthttp://localhost:4321/dbms/dynamodb/http://localhost:4321/dbms/dynamodb/Partition + sort key model, single-table design, on-demand vs provisioned capacity, GSIs, transactions, the cost model.Sun, 24 May 2026 00:00:00 GMTAdvancedsystemSystems & Postmortemsdynamodbnosqlkey-valuepartition-keyawshttp://localhost:4321/dbms/er-relationships-and-constraints/http://localhost:4321/dbms/er-relationships-and-constraints/Relationship types, degree (binary / ternary), cardinality constraints, participation constraints, attributes on relationships.Sun, 24 May 2026 00:00:00 GMTIntermediateconceptData Modelinger-modelrelationshipscardinalityconstraintshttp://localhost:4321/dbms/er-to-relational/http://localhost:4321/dbms/er-to-relational/The standard rules — each entity becomes a table, each relationship becomes a foreign key or junction table, weak entities collapse.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockData Modelinger-modelrelationaltranslationschema-designhttp://localhost:4321/dbms/functional-dependencies/http://localhost:4321/dbms/functional-dependencies/A → B as the unit of schema reasoning; closures; minimal covers; how FDs drive the normal forms.Sun, 24 May 2026 00:00:00 GMTIntermediateconceptNormalizationnormalizationfunctional-dependenciesclosuretheoryhttp://localhost:4321/dbms/gitlab-2017-database-outage/http://localhost:4321/dbms/gitlab-2017-database-outage/A mistaken `rm -rf` on the primary; five backup mechanisms that all failed; the public postmortem everyone should read.Sun, 24 May 2026 00:00:00 GMTFoundationalpostmortemSystems & Postmortemsgitlabbackuppostgresreplicationpostmortemhttp://localhost:4321/dbms/hash-and-bitmap-indexes/http://localhost:4321/dbms/hash-and-bitmap-indexes/Hash indexes for equality lookups, bitmap indexes for low-cardinality columns, the trade-offs vs B-tree.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockStorage & Indexesindexeshashbitmapoltpolaphttp://localhost:4321/dbms/integrity-constraints/http://localhost:4321/dbms/integrity-constraints/Entity integrity, referential integrity, domain constraints, CHECK constraints, and triggers as the catch-all.Sun, 24 May 2026 00:00:00 GMTFoundationalconceptRelational Modelconstraintsintegritycheckforeign-keystriggershttp://localhost:4321/dbms/isolation-levels/http://localhost:4321/dbms/isolation-levels/Read-uncommitted to serializable; the anomalies each prevents (dirty read, non-repeatable, phantom, write skew).Sun, 24 May 2026 00:00:00 GMTIntermediateconceptRelational Modelisolationanomaliesmvccserializablesnapshot-isolationhttp://localhost:4321/dbms/keys-primary-foreign-candidate/http://localhost:4321/dbms/keys-primary-foreign-candidate/What each key is for, how to choose a primary key, why surrogate keys are usually the right default.Sun, 24 May 2026 00:00:00 GMTFoundationalconceptRelational Modelkeysprimary-keyforeign-keysurrogate-keysschema-designhttp://localhost:4321/dbms/joins-inner-outer-cross/http://localhost:4321/dbms/joins-inner-outer-cross/Connecting tables. When LEFT JOIN is the right tool, what FULL OUTER is for, and how CROSS JOIN should be feared.Sun, 24 May 2026 00:00:00 GMTFoundationalbuilding-blockSQLjoinsinner-joinouter-joincross-joinsqlhttp://localhost:4321/dbms/knight-capital-2012/http://localhost:4321/dbms/knight-capital-2012/An old code path enabled by a deploy; loose-state assumptions in a trading system; what 'shared mutable state' costs at scale.Sun, 24 May 2026 00:00:00 GMTFoundationalpostmortemSystems & Postmortemsknight-capitaltradingdeploy-failurefeature-flagpostmortemhttp://localhost:4321/dbms/lsm-trees/http://localhost:4321/dbms/lsm-trees/Memtables, SSTables, compaction. The structure behind LevelDB, RocksDB, Cassandra, ScyllaDB, and DynamoDB's storage.Sun, 24 May 2026 00:00:00 GMTAdvancedbuilding-blockStorage & Indexeslsmstoragewrite-amplificationcompactionrocksdbhttp://localhost:4321/dbms/mvcc/http://localhost:4321/dbms/mvcc/Snapshot isolation, vacuum, the trade-off vs lock-based concurrency. Why Postgres, MySQL InnoDB, and Spanner all use MVCC.Sun, 24 May 2026 00:00:00 GMTAdvancedbuilding-blockStorage & Indexesmvccsnapshot-isolationconcurrencyvacuumisolation-levelshttp://localhost:4321/dbms/mysql-innodb/http://localhost:4321/dbms/mysql-innodb/The B+ tree clustered-index storage engine, group replication, the historical mistakes and how 8.x undid them.Sun, 24 May 2026 00:00:00 GMTIntermediatesystemSystems & Postmortemsmysqlinnodbclustered-indexreplicationoltphttp://localhost:4321/dbms/query-execution-and-plans/http://localhost:4321/dbms/query-execution-and-plans/How the planner reads a query, the cost-based optimizer, EXPLAIN/EXPLAIN ANALYZE, the four operators you'll see most.Sun, 24 May 2026 00:00:00 GMTIntermediateconceptSQLsqlexplainquery-planoptimizerhttp://localhost:4321/dbms/relational-algebra-basics/http://localhost:4321/dbms/relational-algebra-basics/Selection, projection, join, union, difference. The algebra SQL is compiled into.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockRelational Modelrelational-algebraquery-planningjoinsprojectionselectionhttp://localhost:4321/dbms/relational-model-concepts/http://localhost:4321/dbms/relational-model-concepts/Relations, tuples, attributes, domains. Why the relational model won — composability and a closed algebra.Sun, 24 May 2026 00:00:00 GMTFoundationalconceptRelational Modelrelational-modelrelationstuplesattributesalgebrahttp://localhost:4321/dbms/row-store-vs-column-store/http://localhost:4321/dbms/row-store-vs-column-store/Why OLTP is row-oriented and OLAP is column-oriented; the storage layout that explains the performance gap.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockStorage & Indexesstorage-layoutoltpolapcolumnarcompressionhttp://localhost:4321/dbms/select-and-the-where-clause/http://localhost:4321/dbms/select-and-the-where-clause/The shape of every read. Predicate logic, NULL handling, the difference between AND/OR and short-circuit eval.Sun, 24 May 2026 00:00:00 GMTFoundationalbuilding-blockSQLselectwherepredicatesnullthree-valued-logichttp://localhost:4321/dbms/spanner/http://localhost:4321/dbms/spanner/TrueTime, externally consistent transactions, Paxos groups, the breakthrough that made global ACID actually work.Sun, 24 May 2026 00:00:00 GMTAdvancedsystemSystems & Postmortemsspannertruetimepaxosglobal-consistencydistributed-sqlhttp://localhost:4321/dbms/subqueries-and-cte/http://localhost:4321/dbms/subqueries-and-cte/Correlated vs non-correlated subqueries, the readability case for CTEs, recursive CTEs for trees.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockSQLsqlsubquerycterecursivehttp://localhost:4321/dbms/wal-and-recovery/http://localhost:4321/dbms/wal-and-recovery/Why every durable database writes a WAL, ARIES, redo/undo, checkpointing, crash recovery.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockStorage & Indexeswalrecoveryariesdurabilitycheckpointinghttp://localhost:4321/dbms/weak-entities/http://localhost:4321/dbms/weak-entities/Entities whose identity depends on another entity, identifying keys, and where this pattern shows up in real schemas.Sun, 24 May 2026 00:00:00 GMTIntermediateconceptData Modelinger-modelweak-entitiesidentifying-relationshipscomposite-keyshttp://localhost:4321/dbms/why-not-files/http://localhost:4321/dbms/why-not-files/The limits of file-based systems that drove the move to databases — redundancy, integrity, concurrency, recovery.Sun, 24 May 2026 00:00:00 GMTFoundationalconceptFoundationsfoundationsdbmsfile-systemshistoryhttp://localhost:4321/dbms/window-functions/http://localhost:4321/dbms/window-functions/OVER, PARTITION BY, ORDER BY, frame clauses. Running totals, ranks, lag/lead — the part of SQL most engineers underuse.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockSQLsqlwindow-functionsanalyticspartitionhttp://localhost:4321/dbms/b-tree-indexes/http://localhost:4321/dbms/b-tree-indexes/The classic disk-friendly tree, fanout, leaf-page linking, why every relational DBMS defaults to B-tree.Sun, 17 May 2026 00:00:00 GMTIntermediatebuilding-blockStorage & Indexesb-treeindexesstorageoltphttp://localhost:4321/dbms/er-model-basics/http://localhost:4321/dbms/er-model-basics/Entities, attributes, primary keys; entity sets vs entity types; the smallest vocabulary to design a schema.Sun, 17 May 2026 00:00:00 GMTFoundationalconceptData Modelinger-modeldata-modelingschema-designkeyshttp://localhost:4321/dbms/postgresql/http://localhost:4321/dbms/postgresql/Process-per-connection model, MVCC, the planner, extensibility (FDW, custom types), and what makes Postgres the default.Sun, 17 May 2026 00:00:00 GMTIntermediatesystemSystems & Postmortemspostgresqlrdbmsmvccwalreplicationhttp://localhost:4321/dbms/transactions-acid/http://localhost:4321/dbms/transactions-acid/Atomicity, Consistency, Isolation, Durability. What each one promises and where each one bends in practice.Sun, 17 May 2026 00:00:00 GMTFoundationalconceptRelational Modeltransactionsacidisolationdurabilityhttp://localhost:4321/dbms/what-is-a-database/http://localhost:4321/dbms/what-is-a-database/A shared, structured, queryable, persistent collection of data — and the DBMS that gives those four properties teeth.Sun, 17 May 2026 00:00:00 GMTFoundationalconceptFoundationsfoundationsdbmsdefinitionsarchitecture