plainleaf/website/Space Lua/Lua Integrated Query/Grouping.md

#maturity/experimental

The group by and having clauses extend Space Lua/Lua Integrated Query with SQL-style grouping and aggregate filtering.

After group by, each result row has two fields:

• key - the group key (single value or table for multi-key)
• group - a table (array) of all items in that group

The field names used in group by are also available as bare variables in having, select, and order by. Use #group to count items per group.

Note

Note having can only reference group key fields, key, group, aggregate expressions like #group, and aggregate functions like count(). To filter individual rows, use where.

Examples

All examples below use tags.tag.

Group by single key

Group all tags by name:

${query [[ from t = tags.tag group by t.name limit 5 ]]}

Group by multiple keys

Group tags by name and parent together:

${query[[ from t = tags.tag group by t.name, t.parent limit 5 ]]}

Filter groups by count

Only show tags that appear more than 2 times:

${query[[ from t = tags.tag group by t.name having #group > 2 limit 5 ]]}

Find unique tags

Tags appearing exactly once:

${query[[ from t = tags.tag group by t.name having #group == 1 select key ]]}

Filter groups by key value

Only show the group where name is "meta":

${query[[ from tags.tag group by name having name == "meta" ]]}

${query[[ from t = tags.tag group by t.name having t.name == "meta" ]]}

Multi-key having

Groups by name and parent, keep only page-level tags with more than 1 entry:

${query [[ from tags.tag group by name, parent having parent == 'page' and #group > 1 ]]}

where before group by

Filter to page parents first, then group by name:

${query [[ from tags.tag where parent == 'page' group by name ]]}

where, group by and having combined

Filter to page parents, group by name, keep groups with 2+ items: ${query [[ from index.tag 'tag' where parent == 'page' group by name having #group >= 2 ]]}

select name and count

Project each group into a table with name and count: ${query [[ from index.tag 'tag' group by name select { name = name, count = #group } ]]}

select with multi-key

Project both key parts and count:

${query [[ from index.tag 'tag' group by name, parent select { name = name, parent = parent, count = #group } ]]}

Full pipeline: where, group by, having and select

Filter, group, filter groups, then project:

${query [[ from index.tag 'tag' where parent == 'page' or parent == 'task' group by name having #group > 1 select { tag = name, total = #group } ]]}

Order groups by count

Sort groups by size, largest first:

${query [[ from index.tag 'tag' group by name order by #group desc ]]}

Top tags with having, order by, and select

Tags with 2+ occurrences, sorted by count, projected: ${query [[ from index.tag 'tag' group by name having #group >= 2 order by #group desc select { tag = name, count = #group } ]]}

Top N groups with limit

${query [[ from index.tag 'tag' group by name order by #group desc limit 3 ]]}

Full pipeline with limit

Top 5 tags with 2+ uses, showing name and count: ${query [[ from p = index.tag 'tag' group by p.name having #group > 1 select { tag = name, count = #group } ]]}

Multi-key with explicit object variable

Full pipeline with p = binding and two group keys:

${query [[ from p = index.tag 'tag' where p.parent == 'page' group by p.name, p.parent having #group >= 2 order by #group desc select { tag = name, parent = parent, count = #group } ]]}

Access key directly

For single-key grouping, key holds the value directly: ${query [[ from index.tag 'tag' group by name having key == 'meta' ]]}

Access key table for multi-key

For multi-key grouping, key is a table indexed from 1: ${query [[ from index.tag 'tag' group by name, parent having key[1] == 'meta' and key[2] == 'page' ]]}