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Peter Eisentraut 83ea6c5402 Virtual generated columns ... This adds a new variant of generated columns that are computed on read (like a view, unlike the existing stored generated columns, which are computed on write, like a materialized view). The syntax for the column definition is ... GENERATED ALWAYS AS (...) VIRTUAL and VIRTUAL is also optional. VIRTUAL is the default rather than STORED to match various other SQL products. (The SQL standard makes no specification about this, but it also doesn't know about VIRTUAL or STORED.) (Also, virtual views are the default, rather than materialized views.) Virtual generated columns are stored in tuples as null values. (A very early version of this patch had the ambition to not store them at all. But so much stuff breaks or gets confused if you have tuples where a column in the middle is completely missing. This is a compromise, and it still saves space over being forced to use stored generated columns. If we ever find a way to improve this, a bit of pg_upgrade cleverness could allow for upgrades to a newer scheme.) The capabilities and restrictions of virtual generated columns are mostly the same as for stored generated columns. In some cases, this patch keeps virtual generated columns more restricted than they might technically need to be, to keep the two kinds consistent. Some of that could maybe be relaxed later after separate careful considerations. Some functionality that is currently not supported, but could possibly be added as incremental features, some easier than others: - index on or using a virtual column - hence also no unique constraints on virtual columns - extended statistics on virtual columns - foreign-key constraints on virtual columns - not-null constraints on virtual columns (check constraints are supported) - ALTER TABLE / DROP EXPRESSION - virtual column cannot have domain type - virtual columns are not supported in logical replication The tests in generated_virtual.sql have been copied over from generated_stored.sql with the keyword replaced. This way we can make sure the behavior is mostly aligned, and the differences can be visible. Some tests for currently not supported features are currently commented out. Reviewed-by: Jian He <jian.universality@gmail.com> Reviewed-by: Dean Rasheed <dean.a.rasheed@gmail.com> Tested-by: Shlok Kyal <shlok.kyal.oss@gmail.com> Discussion: https://www.postgresql.org/message-id/flat/a368248e-69e4-40be-9c07-6c3b5880b0a6@eisentraut.org		10 months ago
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brin.out	Remove incidental md5() function use from test	1 year ago
btree.out	Add bt_multi_page_stats() function to contrib/pageinspect.	3 years ago
checksum.out	Add an explicit test to catch changes in checksumming calculations.	6 years ago
checksum_1.out	Add an explicit test to catch changes in checksumming calculations.	6 years ago
gin.out	pageinspect: Fix handling of all-zero pages	4 years ago
gist.out	Introduce a new smgr bulk loading facility.	2 years ago
hash.out	pageinspect: Fix failure with hash_bitmap_info() for partitioned indexes	2 years ago
oldextversions.out	Detect version mismatch in brin_page_items	1 year ago
page.out	Virtual generated columns	10 months ago