Details
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Bug
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Status: Closed (View Workflow)
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Major
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Resolution: Fixed
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10.3
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None
Description
Here is the test (picked from derived_cond_pushdown.test in the main suite)
CREATE TABLE t1 (pk1 INT PRIMARY KEY, f INT) ENGINE=Aria; |
INSERT INTO t1 VALUES (1,0),(2,0); |
CREATE TABLE t2 (pk2 INT PRIMARY KEY) ENGINE=Aria; |
INSERT INTO t2 VALUES (1),(2),(3); |
CREATE VIEW v2 AS SELECT pk2, COUNT(*) AS cnt FROM t2 GROUP BY pk2; |
Now when i run this analyze command
MariaDB [test]> ANALYZE FORMAT=JSON SELECT * FROM t1 INNER JOIN v2 ON pk1 = pk2 WHERE f <> 5; |
the output is
| {
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"query_block": {
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"select_id": 1,
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"r_loops": 1,
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"r_total_time_ms": 1.1568,
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"table": {
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"table_name": "t1",
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"access_type": "ALL",
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"possible_keys": ["PRIMARY"],
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"r_loops": 1,
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"rows": 2,
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"r_rows": 2,
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"r_total_time_ms": 0.0677,
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"filtered": 100,
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"r_filtered": 100,
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"attached_condition": "t1.f <> 5"
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},
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"table": {
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"table_name": "<derived2>",
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"access_type": "ref",
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"possible_keys": ["key0"],
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"key": "key0",
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"key_length": "4",
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"used_key_parts": ["pk2"],
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"ref": ["test.t1.pk1"],
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"r_loops": 2,
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"rows": 2,
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"r_rows": 1,
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"r_total_time_ms": 0.7043,
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"filtered": 100,
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"r_filtered": 100,
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"materialized": {
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"query_block": {
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"select_id": 2,
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"r_loops": 2,
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"r_total_time_ms": 0.8569,
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"outer_ref_condition": "t1.pk1 is not null",
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"table": {
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"table_name": "t2",
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"access_type": "eq_ref",
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"possible_keys": ["PRIMARY"],
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"key": "PRIMARY",
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"key_length": "4",
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"used_key_parts": ["pk2"],
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"ref": ["test.t1.pk1"],
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"r_loops": 2,
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"rows": 1,
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"r_rows": 1,
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"r_total_time_ms": 0.0723,
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"filtered": 100,
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"r_filtered": 100,
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"using_index": true
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}
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}
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}
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}
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}
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} |
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So if you look closely at the "outer_ref_condition": "t1.pk1 is not null". But as we see in the create table statement t1.pk1 is a primary key and so it is guaranteed to be NOT NULL so this is a useless condition to have.