Results for “SQL”
Small, practical examples. Search by task or narrow things down below.
Delete one matching row
Remove a selected record and inspect what remains.
DELETE✓ Tested
Delete one row from a practice table
Postgres: Restrict DELETE with a primary-key condition and verify the remaining row count.
Postgres✓ Tested
Delete rows selected by a related table
Postgres: A correlated EXISTS limits the delete to explicitly listed records.
Postgres✓ Tested
Display a fallback for missing data
Postgres: Return a supplied label when a column contains NULL.
Postgres✓ Tested
Distinguish row count from non-null value count
Postgres: COUNT(*) includes every row while COUNT(column) skips NULL values.
Postgres✓ Tested
Divide an ordered result into numbered buckets
Postgres: NTILE distributes rows across buckets; include a unique tie-breaker for deterministic assignment.
Postgres✓ Tested
Enable and use foreign keys
Turn on relationship enforcement for the connection.
foreign keys✓ Tested
Enforce a bounded numeric range
Postgres: A named CHECK constraint keeps numeric values inside an inclusive interval.
Postgres✓ Tested
Enforce a relationship between two columns
Postgres: A row-level CHECK can require a start value to be no greater than an end value.
Postgres✓ Tested
Enforce uniqueness with a dedicated index
Postgres: A unique index rejects a duplicate combination independently of query plans.
Postgres✓ Tested
Expand a JSON array into rows
Iterate array elements using a table-valued function.
json_each✓ Tested
Expand an array into rows
Use WITH ORDINALITY to retain original element order.
unnest✓ Tested