Unique
Description
Deduplicates lower-layer data. During the execution, it traverses all input data, filters duplicate records, and retains only the unique record.
Typical Scenarios
Disable the enable_hashagg parameter and perform the query with DISTINCT.
Examples
Example: Perform the query with DISTINCT.
-- Prepare data. gaussdb=# CREATE TABLE t1 (id INT , number INT); CREATE TABLE gaussdb=# INSERT INTO t1 VALUES(generate_series(1,50), 1); INSERT 0 50 gaussdb=# INSERT INTO t1 VALUES(generate_series(1,50), 2); INSERT 0 50 -- Execution result. gaussdb=# SET enable_hashagg = off; SET gaussdb=# EXPLAIN SELECT DISTINCT t1.id FROM t1; QUERY PLAN ------------------------------------------------------------------ Unique (cost=150.43..161.18 rows=200 width=4) -> Sort (cost=150.43..155.80 rows=2149 width=4) Sort Key: id -> Seq Scan on t1 (cost=0.00..31.49 rows=2149 width=4) (4 rows) -- Drop. gaussdb=# DROP TABLE t1;
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