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| CREATE OR REPLACE FUNCTION hstore_merge(left HSTORE, right HSTORE) RETURNS HSTORE AS $$ | |
| SELECT $1 || $2; | |
| $$ LANGUAGE SQL; | |
| CREATE AGGREGATE hstore_merge (HSTORE) ( | |
| SFUNC = hstore_merge, | |
| STYPE = HSTORE, | |
| INITCOND = '' | |
| ); | |
| -- Example usage: | |
| -- Assume you have a table: | |
| -- | |
| -- CREATE TABLE audit_record ( | |
| -- object_id UUID, | |
| -- modified_values HSTORE, | |
| -- timestamp TIMESTAMP | |
| -- ) | |
| -- | |
| -- where-in you store every modification to a record as an HSTORE | |
| -- containing the fields modified at a specific time, but not | |
| -- the fields that weren't modified. You could use hstore_merge | |
| -- to generate a snapshot of the object at any point in time: | |
| -- | |
| -- SELECT | |
| -- hstore_merge(modified_values) OVER (PARTITION BY object_id ORDER BY timestamp) AS values | |
| -- FROM | |
| -- audit_record | |
| -- WHERE | |
| -- object_id = :object_id AND | |
| -- timestamp <= :timestamp | |
| -- ORDER BY timestamp DESC | |
| -- LIMIT 1 |
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