The snippet library.
Small, practical examples. Search by task or narrow things down below.
Insert only keys absent from a destination
Postgres: NOT EXISTS supports a set-based missing-row insert in a single-writer example.
Postgres✓ Tested
Insert or update on a key conflict
Use a unique key to update an existing row.
ON CONFLICT✓ Tested
Inspect deleted rows
Return values from the rows a DELETE removes.
DELETE✓ Tested
Join a parent to pre-aggregated totals
Postgres: Aggregate the child rows first to produce at most one joined row per parent.
Postgres✓ Tested
Join related rows from two tables
Postgres: Match a category key to its display label with an explicit join condition.
Postgres✓ Tested
Join text rows in a chosen order
Combine values using string_agg.
string_agg✓ Tested
Join through a lookup table
Postgres: Use explicit aliases and join keys when enriching records through two relationships.
Postgres✓ Tested
Keep children while clearing a deleted relationship
Postgres: ON DELETE SET NULL requires a nullable foreign-key column.
Postgres✓ Tested
Keep parent rows while filtering joined children
Postgres: Put a child filter in ON when unmatched parents must remain in the result.
Postgres✓ Tested
Keep rows matching a condition
Postgres: Use WHERE to select rows with a particular category.
Postgres✓ Tested
List unordered pairs without duplicate reversals
Postgres: Join using an increasing key comparison to omit self-pairs and reversed duplicates.
Postgres✓ Tested
Make a pair of columns unique together
Postgres: A composite primary key permits repeated individual values while forbidding a duplicate combination.
Postgres✓ Tested