Why JOIN Multiplies Rows: Matching Keys, Constraints and Output Grain
Diagnose repeated JOIN rows by counting matching keys, checking constraints and choosing whether the result should contain orders, items or summaries.
SQL / JOIN / PostgreSQL
TECHNOLOGY / KNOWLEDGE / PRACTICE
Search results: constraints
Materials on AI, Python, Git, SQL, SAP/ERP, statistics and time series: explanations, examples, practical tips, sources and applicability limits.
Every word must appear in the article. Use quotes for an exact phrase.
PostgreSQL foreign keys: NO ACTION timing and selective SET NULL
A closer look at explicitly deferred NO ACTION checks and clearing only the optional component of a composite foreign key. These details complement the basic choice between RESTRICT, CASCADE and SET NULL.
postgresql / foreign-key / on-delete / data-retention / cascade / restrict / set-null / referential-integrity
Choose a PostgreSQL foreign-key deletion policy without losing the wrong rows
Compare RESTRICT, CASCADE and SET NULL using a small isolated example, then check the actual constraint and dependent rows before changing real data.
PostgreSQL / SQL / Foreign keys / Transactions
PostgreSQL INSERT ON CONFLICT: Correct Upsert with Unique Targets, DO NOTHING vs DO UPDATE
Use ON CONFLICT to atomically insert or update rows based on unique constraints. Specify the exact conflict target, handle duplicate input rows, and understand that excluded values replace, not accumulate.
postgresql / sql / upsert / insert / on-conflict / unique-constraint / concurrency / database
How BEGIN, COMMIT, and ROLLBACK Combine Multiple Changes into a Single Operation in PostgreSQL
Transactions in PostgreSQL allow grouping SQL operations into atomic blocks using the commands BEGIN, COMMIT, and ROLLBACK. This ensures data integrity: either all changes are applied or none at all. The mechanism is based on ACID principles - atomicity, consistency, isolation, and durability.
PostgreSQL / transactions / BEGIN / COMMIT / ROLLBACK / ACID / savepoint