Members per surname initial
left(text, n) returns the first n characters. Grouping on an expression works like grouping on a column.
task
For each first letter of the surname, give the letter (initial) and how many members have it. Order by initial.
Play
lessons
aggregates
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btree
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- [ ] is not distinct from reaches the index
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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
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- [ ] the visibility map after vacuum
- [ ] vacuum full gives the space back
- [ ] which table would autovacuum pick
m5-hot
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p10-partitioning
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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
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set-operations
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wal
what-changed-in-19
- [ ] aggregate support clause
- [ ] base64url token
- [ ] boss pg19 table repair
- [ ] check not enforced promote
- [ ] checkpoint options
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- [ ] 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
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- [ ] inet gist default
- [ ] is json domain
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- [ ] repack concurrently
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- [ ] repack partitioned needs index
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- [ ] stemmer dictionaries
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- [ ] temporal oncall
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- [ ] virtual set expression
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