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| author | Peter Eisentraut <peter@eisentraut.org> | 2019-03-30 08:13:09 +0100 |
|---|---|---|
| committer | Peter Eisentraut <peter@eisentraut.org> | 2019-03-30 08:15:57 +0100 |
| commit | fc22b6623b6b3bab3cb057ccd282c2bfad1a0b30 (patch) | |
| tree | cda5092955ece5d547d5517ed56a3d480f199d25 /src/backend/utils/cache/lsyscache.c | |
| parent | 6b8b5364ddd0e4d882562615c6b6c28638ade9f2 (diff) | |
Generated columns
This is an SQL-standard feature that allows creating columns that are
computed from expressions rather than assigned, similar to a view or
materialized view but on a column basis.
This implements one kind of generated column: stored (computed on
write). Another kind, virtual (computed on read), is planned for the
future, and some room is left for it.
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Pavel Stehule <pavel.stehule@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/b151f851-4019-bdb1-699e-ebab07d2f40a@2ndquadrant.com
Diffstat (limited to 'src/backend/utils/cache/lsyscache.c')
| -rw-r--r-- | src/backend/utils/cache/lsyscache.c | 33 |
1 files changed, 33 insertions, 0 deletions
diff --git a/src/backend/utils/cache/lsyscache.c b/src/backend/utils/cache/lsyscache.c index 59e6bcd856c..10895567c09 100644 --- a/src/backend/utils/cache/lsyscache.c +++ b/src/backend/utils/cache/lsyscache.c @@ -822,6 +822,39 @@ get_attnum(Oid relid, const char *attname) } /* + * get_attgenerated + * + * Given the relation id and the attribute name, + * return the "attgenerated" field from the attribute relation. + * + * Errors if not found. + * + * Since not generated is represented by '\0', this can also be used as a + * Boolean test. + */ +char +get_attgenerated(Oid relid, AttrNumber attnum) +{ + HeapTuple tp; + + tp = SearchSysCache2(ATTNUM, + ObjectIdGetDatum(relid), + Int16GetDatum(attnum)); + if (HeapTupleIsValid(tp)) + { + Form_pg_attribute att_tup = (Form_pg_attribute) GETSTRUCT(tp); + char result; + + result = att_tup->attgenerated; + ReleaseSysCache(tp); + return result; + } + else + elog(ERROR, "cache lookup failed for attribute %d of relation %u", + attnum, relid); +} + +/* * get_atttype * * Given the relation OID and the attribute number with the relation, |