Monthly cohorts
A cohort groups customers by when they started. Compare signup month with the month of the first order.
task
Count customers by signup month and by month of their first order.
Play
lessons
aggregates
amcheck
analytics
btree
- [ ] a lookup reads few pages
- [ ] b tree meta page
- [ ] boss count a group from the index
- [ ] brin ranges
- [ ] gin pending list
- [ ] index only scans and heap fetches
- [ ] is not distinct from reaches the index
- [ ] physical correlation
- [ ] random inserts leave leaf pages loose
- [ ] skip scan on a b tree
- [ ] walk the root page
buffers
changing-data
copy
ctes-recursion
dates
explain
expressions
full-text-search
indexes
intro
joins
jsonb
locks
m1-catalogs
- [ ] boss one row about a table
- [ ] clear one extended statistics object
- [ ] clear statistics of a missing table
- [ ] column layout in pg attribute
- [ ] count your table s forks
- [ ] extended statistics on virtual generated columns
- [ ] pg stats knows the table oid
- [ ] statistics on a boolean function
- [ ] the index behind a primary key
- [ ] what pg class says about a table
m2-heap-pages
m3-mvcc
m4-vacuum
- [ ] a fresh file after repack
- [ ] a partitioned table needs an index name
- [ ] a read sets all visible without vacuum
- [ ] boss one vacuum cycle
- [ ] dead item memory in vacuum verbose
- [ ] line pointers across delete and vacuum
- [ ] relfrozenxid advances
- [ ] repack concurrently
- [ ] repack using index orders the heap
- [ ] the visibility map after vacuum
- [ ] vacuum full gives the space back
- [ ] which table would autovacuum pick
m5-hot
m6-toast
null
p10-partitioning
p11-rls-roles
p8-functions-triggers
p9-views
planner
- [ ] an impossible predicate
- [ ] coalesce stops at the first not null argument
- [ ] incremental sort under append
- [ ] is not distinct from reaches the index
- [ ] is null on any not null column of the inner side
- [ ] memoize under an anti join
- [ ] read stream counters in explain io
- [ ] read the memoize estimate
- [ ] turn eager aggregation off
ranges
schema-design
sequences-identity-uuid
set-operations
statistics
subqueries
transactions
types
wal
what-changed-in-19
- [ ] aggregate support clause
- [ ] base64url token
- [ ] boss pg19 table repair
- [ ] check not enforced promote
- [ ] checkpoint options
- [ ] conflict select needs returning
- [ ] copy header n
- [ ] copy json header error
- [ ] copy multiline header out
- [ ] copy partitioned roundtrip
- [ ] copy set null
- [ ] distinct from null folding
- [ ] eager aggregate
- [ ] grant granted by
- [ ] group subquery expr
- [ ] group subquery grouping
- [ ] inet gist default
- [ ] is json domain
- [ ] jit off
- [ ] json array empty
- [ ] jsonpath colors upper
- [ ] no crlf in names
- [ ] notin antijoin
- [ ] notin nullable
- [ ] oid8 validation
- [ ] psql display true
- [ ] psql search path prompt
- [ ] random dates
- [ ] regdatabase lookup
- [ ] repack concurrently
- [ ] repack index order
- [ ] repack partitioned needs index
- [ ] schema forward fk
- [ ] scs always on
- [ ] search path null
- [ ] skip scan
- [ ] stemmer dictionaries
- [ ] subscription server
- [ ] temporal oncall
- [ ] tid pages
- [ ] uuid from md5
- [ ] uuid from sha256 error
- [ ] virtual default
- [ ] virtual set expression
- [ ] virtual set expression violation
- [ ] wait for lsn
- [ ] win ignore rank error
editor
results
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