Results for “post”
Small, practical examples. Search by task or narrow things down below.
Filter groups after aggregation
Postgres: Use HAVING to test a group’s calculated total.
Postgres✓ Tested
Filter rows before grouping
Postgres: WHERE limits the rows contributing to the aggregate; it differs from filtering completed groups with HAVING.
Postgres✓ Tested
Find missing values with IS NULL
Postgres: Use IS NULL rather than equality to test for missing data.
Postgres✓ Tested
Find parents whose every child meets a rule
Postgres: Combine existence with the absence of a violating child to exclude parents with no children.
Postgres✓ Tested
Find parents with at least two child rows
Postgres: Use a correlated count when testing a per-parent threshold.
Postgres✓ Tested
Find records without any related rows
Postgres: NOT EXISTS avoids the NULL pitfalls of NOT IN when the subquery column can be missing.
Postgres✓ Tested
Find rows in the first result but not the second
Postgres: EXCEPT calculates a distinct result-set difference.
Postgres✓ Tested
Find rows shared by two query results
Postgres: INTERSECT compares complete selected rows and removes duplicates.
Postgres✓ Tested
Find the second-highest distinct value
Postgres: Select the maximum below the overall maximum to skip ties at the top.
Postgres✓ Tested
Generate every combination of two sets
Postgres: CROSS JOIN creates one result per possible pair, so the output size is the product of the input sizes.
Postgres✓ Tested
Give a result column a readable name
Postgres: Use AS to label a computed result column.
Postgres✓ Tested
Group by more than one field
Postgres: Each distinct combination of grouping fields produces its own row.
Postgres✓ Tested