mysql中cost对比测试

1.数据库表

复制表

2.执行select c_id from customer where c_discount = 0.35;后，explain对比

3.optimizer_trace比较
原表

{"steps": [{"join_preparation": {"select#": 1,"steps": [{"expanded_query": "/* select#1 */ select `customer`.`c_id` AS `c_id` from `customer` where (`customer`.`c_discount` = 0.35)"}]}},{"join_optimization": {"select#": 1,"steps": [{"condition_processing": {"condition": "WHERE","original_condition": "(`customer`.`c_discount` = 0.35)","steps": [{"transformation": "equality_propagation","resulting_condition": "multiple equal(0.35, `customer`.`c_discount`)"},{"transformation": "constant_propagation","resulting_condition": "multiple equal(0.35, `customer`.`c_discount`)"},{"transformation": "trivial_condition_removal","resulting_condition": "multiple equal(0.35, `customer`.`c_discount`)"}]}},{"substitute_generated_columns": {}},{"table_dependencies": [{"table": "`customer`","row_may_be_null": false,"map_bit": 0,"depends_on_map_bits": []}]},{"ref_optimizer_key_uses": []},{"rows_estimation": [{"table": "`customer`","table_scan": {"rows": 289371,"cost": 11504}}]},{"considered_execution_plans": [{"plan_prefix": [],"table": "`customer`","best_access_path": {"considered_access_paths": [{"rows_to_scan": 289371,"filtering_effect": [],"final_filtering_effect": 0.1,"access_type": "scan","resulting_rows": 28937,"cost": 40441,"chosen": true}]},"condition_filtering_pct": 100,"rows_for_plan": 28937,"cost_for_plan": 40441,"chosen": true}]},{"attaching_conditions_to_tables": {"original_condition": "(`customer`.`c_discount` = 0.35)","attached_conditions_computation": [],"attached_conditions_summary": [{"table": "`customer`","attached": "(`customer`.`c_discount` = 0.35)"}]}},{"refine_plan": [{"table": "`customer`"}]}]}},{"join_explain": {"select#": 1,"steps": []}}]
}

复制表

{"steps": [{"join_preparation": {"select#": 1,"steps": [{"expanded_query": "/* select#1 */ select `customer_new`.`c_id` AS `c_id` from `customer_new` where (`customer_new`.`c_discount` = 0.35)"}]}},{"join_optimization": {"select#": 1,"steps": [{"condition_processing": {"condition": "WHERE","original_condition": "(`customer_new`.`c_discount` = 0.35)","steps": [{"transformation": "equality_propagation","resulting_condition": "multiple equal(0.35, `customer_new`.`c_discount`)"},{"transformation": "constant_propagation","resulting_condition": "multiple equal(0.35, `customer_new`.`c_discount`)"},{"transformation": "trivial_condition_removal","resulting_condition": "multiple equal(0.35, `customer_new`.`c_discount`)"}]}},{"substitute_generated_columns": {}},{"table_dependencies": [{"table": "`customer_new`","row_may_be_null": false,"map_bit": 0,"depends_on_map_bits": []}]},{"ref_optimizer_key_uses": [{"table": "`customer_new`","field": "c_discount","equals": "0.35","null_rejecting": false}]},{"rows_estimation": [{"table": "`customer_new`","range_analysis": {"table_scan": {"rows": 285901,"cost": 41760},"potential_range_indexes": [{"index": "PRIMARY","usable": false,"cause": "not_applicable"},{"index": "c_d_1","usable": true,"key_parts": ["c_discount","c_w_id","c_d_id","c_id"]}],"best_covering_index_scan": {"index": "c_d_1","cost": 28939,"chosen": true},"setup_range_conditions": [],"group_index_range": {"chosen": false,"cause": "not_group_by_or_distinct"},"analyzing_range_alternatives": {"range_scan_alternatives": [{"index": "c_d_1","ranges": ["0.35 <= c_discount <= 0.35"],"index_dives_for_eq_ranges": true,"rowid_ordered": true,"using_mrr": false,"index_only": true,"rows": 5822,"cost": 590.29,"chosen": true}],"analyzing_roworder_intersect": {"usable": false,"cause": "too_few_roworder_scans"}},"chosen_range_access_summary": {"range_access_plan": {"type": "range_scan","index": "c_d_1","rows": 5822,"ranges": ["0.35 <= c_discount <= 0.35"]},"rows_for_plan": 5822,"cost_for_plan": 590.29,"chosen": true}}}]},{"considered_execution_plans": [{"plan_prefix": [],"table": "`customer_new`","best_access_path": {"considered_access_paths": [{"access_type": "ref","index": "c_d_1","rows": 5822,"cost": 590.28,"chosen": true},{"access_type": "range","range_details": {"used_index": "c_d_1"},"chosen": false,"cause": "heuristic_index_cheaper"}]},"condition_filtering_pct": 100,"rows_for_plan": 5822,"cost_for_plan": 590.28,"chosen": true}]},{"attaching_conditions_to_tables": {"original_condition": "(`customer_new`.`c_discount` = 0.35)","attached_conditions_computation": [],"attached_conditions_summary": [{"table": "`customer_new`","attached": null}]}},{"refine_plan": [{"table": "`customer_new`"}]}]}},{"join_explain": {"select#": 1,"steps": []}}]
}

其中原表的cost

带索引表中table_scan的值

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