Results for “Postgres”
Small, practical examples. Search by task or narrow things down below.
Count rows per category
Aggregate rows sharing the same category.
GROUP BY✓ Tested
Count rows satisfying separate conditions
SQL: SUM over CASE expressions calculates several conditional counts in one scan.
SQL✓ Tested
Count the rows in a table
SQL: COUNT(*) includes every row, including rows with NULL columns.
SQL✓ Tested
Create a table and insert its first row
SQL: Define column types and a primary key, then insert one row using an explicit column list.
SQL✓ Tested
Create an index for an equality filter
SQL: A nonunique index can support lookups on a frequently filtered column.
SQL✓ Tested
Create an index matching filter and ordering columns
SQL: Place the equality-filter column before the ordering column in this composite index.
SQL✓ Tested
Delete one matching row
Remove a selected record and inspect what remains.
DELETE✓ Tested
Delete one row from a practice table
SQL: Restrict DELETE with a primary-key condition and verify the remaining row count.
SQL✓ Tested
Delete rows selected by a related table
SQL: A correlated EXISTS limits the delete to explicitly listed records.
SQL✓ Tested
Display a fallback for missing data
SQL: Return a supplied label when a column contains NULL.
SQL✓ Tested
Distinguish row count from non-null value count
SQL: COUNT(*) includes every row while COUNT(column) skips NULL values.
SQL✓ Tested
Divide an ordered result into numbered buckets
SQL: NTILE distributes rows across buckets; include a unique tie-breaker for deterministic assignment.
SQL✓ Tested