MySQL ORDER BY主键id加LIMIT限制走错索引

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report_product_sales_data 表数据量 2800 万；
经测试，在当前数据量情况下，order by 主键 id，limit 最大到 49 的时候可以用到索引 report_product_sales_data_hq_code_orgz_id_index，大于 49 时就走 PRIMARY 主键索引。

CREATE TABLE `report_product_sales_data` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT COMMENT ‘ID’,
`hq_code` char(16) COLLATE utf8_unicode_ci NOT NULL COMMENT ‘ 公司编码 ’,
`product_id` int(10) unsigned NOT NULL COMMENT ‘ 商品 ID’,
`orgz_id` int(10) unsigned NOT NULL COMMENT ‘ 组织 ID’,
`sales_num` double(16,3) NOT NULL COMMENT ‘ 销售数量 ’,
`report_date` date NOT NULL COMMENT ‘ 报表日期 ’,
`status` tinyint(4) NOT NULL DEFAULT ‘0’ COMMENT ‘ 状态: 0. 未日结，1. 已日结 ’,
`created_at` timestamp NULL DEFAULT NULL,
`updated_at` timestamp NULL DEFAULT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `report_product_sales_data_unique` (`hq_code`,`report_date`,`orgz_id`,`product_id`),
KEY `report_product_sales_data_hq_code_orgz_id_index` (`hq_code`,`orgz_id`,`report_date`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci COMMENT=’ 商品日营业数据表 ’;

Explain 命令查看执行计划

— 批量查询耗时 154ms
select product_id, sales_num, report_date from `report_product_sales_data`
where `hq_code` = ‘000030’
and `orgz_id` = 229
and `product_id` in (11453,11472,11487,11446,11456,12088,11433,114170,11479,11491,11485,11482,70672,68998,154298,11435,11481,11515,122573,167938)
and `report_date` > ‘2018-05-11’ order by id desc
limit 320;
— explain 结果如下
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE report_product_sales_data range report_product_sales_data_unique,report_product_sales_data_hq_code_orgz_id_index report_product_sales_data_hq_code_orgz_id_index 55 NULL 37088 Using index condition; Using where; Using filesort– 批量查询耗时 397ms
select product_id, sales_num, report_date from `report_product_sales_data`
where `hq_code` = ‘000030’
and `orgz_id` = 229
and `product_id` in (11453,11472,11487,11446,11456,12088,11433,114170,11479,11491,11485,11482,70672,68998,154298,11435,11481,11515,122573,167938)
and `report_date` > ‘2018-05-11’
order by `id` desc limit 10;
— explain 结果如下
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE report_product_sales_data index report_product_sales_data_unique,report_product_sales_data_hq_code_orgz_id_index PRIMARY 4 NULL 7624 Using where

— 开启优化器跟踪
set session optimizer_trace=’enabled=on’;
— 在执行完查询语句后，在执行以下的 select 语句可以查看具体的优化器执行过程
select * from information_schema.optimizer_trace;– 对于这条走了预期 report_product_sales_data_hq_code_orgz_id_index 索引的查询，我们看下优化器的执行过程
select product_id, sales_num, report_date from `report_product_sales_data`
where `hq_code` = ‘000030’
and `orgz_id` = 229
and `product_id` in (11453,11472,11487,11446,11456,12088,11433,114170,11479,11491,11485,11482,70672,68998,154298,11435,11481,11515,122573,167938)
and `report_date` > ‘2018-05-11’ order by id desc
limit 320;– 看下 trace 部分
{
“steps”: [
{
“join_preparation”: {
“select#”: 1,
“steps”: [
{
“expanded_query”: “/* select#1 */ select `report_product_sales_data`.`product_id` AS `product_id`,`report_product_sales_data`.`sales_num` AS `sales_num`,`report_product_sales_data`.`report_date` AS `report_date` from `report_product_sales_data` where ((`report_product_sales_data`.`hq_code` = ‘000030’) and (`report_product_sales_data`.`orgz_id` = 229) and (`report_product_sales_data`.`product_id` in (11453,11472,11487,11446,11456,12088,11433,114170,11479,11491,11485,11482,70672,68998,154298,11435,11481,11515,122573,167938)) and (`report_product_sales_data`.`report_date` > ‘2018-05-11’)) order by `report_product_sales_data`.`id` desc limit 320”
}
]
}
},
{
“join_optimization”: {
“select#”: 1,
“steps”: [
{
“condition_processing”: {
“condition”: “WHERE”,
“original_condition”: “((`report_product_sales_data`.`hq_code` = ‘000030’) and (`report_product_sales_data`.`orgz_id` = 229) and (`report_product_sales_data`.`product_id` in (11453,11472,11487,11446,11456,12088,11433,114170,11479,11491,11485,11482,70672,68998,154298,11435,11481,11515,122573,167938)) and (`report_product_sales_data`.`report_date` > ‘2018-05-11’))”,
“steps”: [
{
“transformation”: “equality_propagation”,
“resulting_condition”: “((`report_product_sales_data`.`hq_code` = ‘000030’) and (`report_product_sales_data`.`product_id` in (11453,11472,11487,11446,11456,12088,11433,114170,11479,11491,11485,11482,70672,68998,154298,11435,11481,11515,122573,167938)) and (`report_product_sales_data`.`report_date` > ‘2018-05-11’) and multiple equal(229, `report_product_sales_data`.`orgz_id`))”
},
{
“transformation”: “constant_propagation”,
“resulting_condition”: “((`report_product_sales_data`.`hq_code` = ‘000030’) and (`report_product_sales_data`.`product_id` in (11453,11472,11487,11446,11456,12088,11433,114170,11479,11491,11485,11482,70672,68998,154298,11435,11481,11515,122573,167938)) and (`report_product_sales_data`.`report_date` > ‘2018-05-11’) and multiple equal(229, `report_product_sales_data`.`orgz_id`))”
},
{
“transformation”: “trivial_condition_removal”,
“resulting_condition”: “((`report_product_sales_data`.`hq_code` = ‘000030’) and (`report_product_sales_data`.`product_id` in (11453,11472,11487,11446,11456,12088,11433,114170,11479,11491,11485,11482,70672,68998,154298,11435,11481,11515,122573,167938)) and (`report_product_sales_data`.`report_date` > ‘2018-05-11’) and multiple equal(229, `report_product_sales_data`.`orgz_id`))”
}
]
}
},
{
“table_dependencies”: [
{
“table”: “`report_product_sales_data`”,
“row_may_be_null”: false,
“map_bit”: 0,
“depends_on_map_bits”: [
]
}
]
},
{
“ref_optimizer_key_uses”: [
{
“table”: “`report_product_sales_data`”,
“field”: “hq_code”,
“equals”: “‘000030′”,
“null_rejecting”: false
},
{
“table”: “`report_product_sales_data`”,
“field”: “hq_code”,
“equals”: “‘000030′”,
“null_rejecting”: false
},
{
“table”: “`report_product_sales_data`”,
“field”: “orgz_id”,
“equals”: “229”,
“null_rejecting”: false
}
]
},
{
“rows_estimation”: [
{
“table”: “`report_product_sales_data`”,
“range_analysis”: {
“table_scan”: {
“rows”: 28276082,
“cost”: 6.14e6
},
“potential_range_indices”: [
{
“index”: “PRIMARY”,
“usable”: false,
“cause”: “not_applicable”
},
{
“index”: “report_product_sales_data_unique”,
“usable”: true,
“key_parts”: [
“hq_code”,
“report_date”,
“orgz_id”,
“product_id”
]
},
{
“index”: “report_product_sales_data_hq_code_orgz_id_index”,
“usable”: true,
“key_parts”: [
“hq_code”,
“orgz_id”,
“report_date”,
“id”
]
}
],
“setup_range_conditions”: [
],
“group_index_range”: {
“chosen”: false,
“cause”: “not_group_by_or_distinct”
},
“analyzing_range_alternatives”: {
“range_scan_alternatives”: [
{
“index”: “report_product_sales_data_unique”,
“ranges”: [
“000030 <= hq_code <= 000030 AND 2018-05-11 < report_date”
],
“index_dives_for_eq_ranges”: true,
“rowid_ordered”: false,
“using_mrr”: false,
“index_only”: false,
“rows”: 1848962,
“cost”: 2.22e6,
“chosen”: true
},
{
“index”: “report_product_sales_data_hq_code_orgz_id_index”,
“ranges”: [
“000030 <= hq_code <= 000030 AND 229 <= orgz_id <= 229 AND 2018-05-11 < report_date”
],
“index_dives_for_eq_ranges”: true,
“rowid_ordered”: false,
“using_mrr”: false,
“index_only”: false,
“rows”: 37088,
“cost”: 44507,
“chosen”: true
}
],
“analyzing_roworder_intersect”: {
“usable”: false,
“cause”: “too_few_roworder_scans”
}
},
“chosen_range_access_summary”: {
“range_access_plan”: {
“type”: “range_scan”,
“index”: “report_product_sales_data_hq_code_orgz_id_index”,
“rows”: 37088,
“ranges”: [
“000030 <= hq_code <= 000030 AND 229 <= orgz_id <= 229 AND 2018-05-11 < report_date”
]
},
“rows_for_plan”: 37088,
“cost_for_plan”: 44507,
“chosen”: true
}
}
}
]
},
{
“considered_execution_plans”: [
{
“plan_prefix”: [
],
“table”: “`report_product_sales_data`”,
“best_access_path”: {
“considered_access_paths”: [
{
“access_type”: “ref”,
“index”: “report_product_sales_data_unique”,
“rows”: 1.85e6,
“cost”: 1.82e6,
“chosen”: true
},
{
// 可以看到选择 report_product_sales_data_hq_code_orgz_id_index 这个索引时 cost 最小
“access_type”: “ref”,
“index”: “report_product_sales_data_hq_code_orgz_id_index”,
“rows”: 37088,
“cost”: 44506,
“chosen”: true
},
{
“access_type”: “range”,
“rows”: 27816,
“cost”: 51924,
“chosen”: false
}
]
},
“cost_for_plan”: 44506,
“rows_for_plan”: 37088,
“chosen”: true
}
]
},
{
“attaching_conditions_to_tables”: {
“original_condition”: “((`report_product_sales_data`.`orgz_id` = 229) and (`report_product_sales_data`.`hq_code` = ‘000030’) and (`report_product_sales_data`.`product_id` in (11453,11472,11487,11446,11456,12088,11433,114170,11479,11491,11485,11482,70672,68998,154298,11435,11481,11515,122573,167938)) and (`report_product_sales_data`.`report_date` > ‘2018-05-11’))”,
“attached_conditions_computation”: [
{
“access_type_changed”: {
“table”: “`report_product_sales_data`”,
“index”: “report_product_sales_data_hq_code_orgz_id_index”,
“old_type”: “ref”,
“new_type”: “range”,
“cause”: “uses_more_keyparts”
}
}
],
“attached_conditions_summary”: [
{
“table”: “`report_product_sales_data`”,
“attached”: “((`report_product_sales_data`.`orgz_id` = 229) and (`report_product_sales_data`.`hq_code` = ‘000030’) and (`report_product_sales_data`.`product_id` in (11453,11472,11487,11446,11456,12088,11433,114170,11479,11491,11485,11482,70672,68998,154298,11435,11481,11515,122573,167938)) and (`report_product_sales_data`.`report_date` > ‘2018-05-11’))”
}
]
}
},
{
“clause_processing”: {
“clause”: “ORDER BY”,
“original_clause”: “`report_product_sales_data`.`id` desc”,
“items”: [
{
“item”: “`report_product_sales_data`.`id`”
}
],
“resulting_clause_is_simple”: true,
“resulting_clause”: “`report_product_sales_data`.`id` desc”
}
},
{
“refine_plan”: [
{
“table”: “`report_product_sales_data`”,
“pushed_index_condition”: “((`report_product_sales_data`.`orgz_id` = 229) and (`report_product_sales_data`.`hq_code` = ‘000030’) and (`report_product_sales_data`.`report_date` > ‘2018-05-11’))”,
“table_condition_attached”: “(`report_product_sales_data`.`product_id` in (11453,11472,11487,11446,11456,12088,11433,114170,11479,11491,11485,11482,70672,68998,154298,11435,11481,11515,122573,167938))”,
“access_type”: “range”
}
]
},
{
“reconsidering_access_paths_for_index_ordering”: {
// 到了 order by id 这边时，MySQL 也没有改变执行计划，还是选择了 report_product_sales_data_hq_code_orgz_id_index 索引
“clause”: “ORDER BY”,
“index_order_summary”: {
“table”: “`report_product_sales_data`”,
“index_provides_order”: false,
“order_direction”: “undefined”,
“index”: “report_product_sales_data_hq_code_orgz_id_index”,
“plan_changed”: false
}
}
}
]
}
},
{
“join_execution”: {
“select#”: 1,
“steps”: [
{
“filesort_information”: [
{
“direction”: “desc”,
“table”: “`report_product_sales_data`”,
“field”: “id”
}
],
“filesort_priority_queue_optimization”: {
“limit”: 320,
“rows_estimate”: 61044633,
“row_size”: 76,
“memory_available”: 262144,
“chosen”: true
},
“filesort_execution”: [
],
“filesort_summary”: {
“rows”: 321,
“examined_rows”: 15768,
“number_of_tmp_files”: 0,
“sort_buffer_size”: 26964,
“sort_mode”: “<sort_key, additional_fields>”
}
}
]
}
}
]
}– 对于这条走了非预期 PRIMARY 主键索引的查询，我们看下优化器的执行过程
select product_id, sales_num, report_date from `report_product_sales_data`
where `hq_code` = ‘000030’
and `orgz_id` = 229
and `product_id` in (11453,11472,11487,11446,11456,12088,11433,114170,11479,11491,11485,11482,70672,68998,154298,11435,11481,11515,122573,167938)
and `report_date` > ‘2018-05-11’ order by id desc
limit 10;– 看下 trace 部分
{
“steps”: [
{
“join_preparation”: {
“select#”: 1,
“steps”: [
{
“expanded_query”: “/* select#1 */ select `report_product_sales_data`.`product_id` AS `product_id`,`report_product_sales_data`.`sales_num` AS `sales_num`,`report_product_sales_data`.`report_date` AS `report_date` from `report_product_sales_data` where ((`report_product_sales_data`.`hq_code` = ‘000030’) and (`report_product_sales_data`.`orgz_id` = 229) and (`report_product_sales_data`.`product_id` in (11453,11472,11487,11446,11456,12088,11433,114170,11479,11491,11485,11482,70672,68998,154298,11435,11481,11515,122573,167938)) and (`report_product_sales_data`.`report_date` > ‘2018-05-11’)) order by `report_product_sales_data`.`id` desc limit 10”
}
]
}
},
{
“join_optimization”: {
“select#”: 1,
“steps”: [
{
“condition_processing”: {
“condition”: “WHERE”,
“original_condition”: “((`report_product_sales_data`.`hq_code` = ‘000030’) and (`report_product_sales_data`.`orgz_id` = 229) and (`report_product_sales_data`.`product_id` in (11453,11472,11487,11446,11456,12088,11433,114170,11479,11491,11485,11482,70672,68998,154298,11435,11481,11515,122573,167938)) and (`report_product_sales_data`.`report_date` > ‘2018-05-11’))”,
“steps”: [
{
“transformation”: “equality_propagation”,
“resulting_condition”: “((`report_product_sales_data`.`hq_code` = ‘000030’) and (`report_product_sales_data`.`product_id` in (11453,11472,11487,11446,11456,12088,11433,114170,11479,11491,11485,11482,70672,68998,154298,11435,11481,11515,122573,167938)) and (`report_product_sales_data`.`report_date` > ‘2018-05-11’) and multiple equal(229, `report_product_sales_data`.`orgz_id`))”
},
{
“transformation”: “constant_propagation”,
“resulting_condition”: “((`report_product_sales_data`.`hq_code` = ‘000030’) and (`report_product_sales_data`.`product_id` in (11453,11472,11487,11446,11456,12088,11433,114170,11479,11491,11485,11482,70672,68998,154298,11435,11481,11515,122573,167938)) and (`report_product_sales_data`.`report_date` > ‘2018-05-11’) and multiple equal(229, `report_product_sales_data`.`orgz_id`))”
},
{
“transformation”: “trivial_condition_removal”,
“resulting_condition”: “((`report_product_sales_data`.`hq_code` = ‘000030’) and (`report_product_sales_data`.`product_id` in (11453,11472,11487,11446,11456,12088,11433,114170,11479,11491,11485,11482,70672,68998,154298,11435,11481,11515,122573,167938)) and (`report_product_sales_data`.`report_date` > ‘2018-05-11’) and multiple equal(229, `report_product_sales_data`.`orgz_id`))”
}
]
}
},
{
“table_dependencies”: [
{
“table”: “`report_product_sales_data`”,
“row_may_be_null”: false,
“map_bit”: 0,
“depends_on_map_bits”: [
]
}
]
},
{
“ref_optimizer_key_uses”: [
{
“table”: “`report_product_sales_data`”,
“field”: “hq_code”,
“equals”: “‘000030′”,
“null_rejecting”: false
},
{
“table”: “`report_product_sales_data`”,
“field”: “hq_code”,
“equals”: “‘000030′”,
“null_rejecting”: false
},
{
“table”: “`report_product_sales_data`”,
“field”: “orgz_id”,
“equals”: “229”,
“null_rejecting”: false
}
]
},
{
“rows_estimation”: [
{
“table”: “`report_product_sales_data`”,
“range_analysis”: {
“table_scan”: {
“rows”: 28276082,
“cost”: 6.14e6
},
“potential_range_indices”: [
{
“index”: “PRIMARY”,
“usable”: false,
“cause”: “not_applicable”
},
{
“index”: “report_product_sales_data_unique”,
“usable”: true,
“key_parts”: [
“hq_code”,
“report_date”,
“orgz_id”,
“product_id”
]
},
{
“index”: “report_product_sales_data_hq_code_orgz_id_index”,
“usable”: true,
“key_parts”: [
“hq_code”,
“orgz_id”,
“report_date”,
“id”
]
}
],
“setup_range_conditions”: [
],
“group_index_range”: {
“chosen”: false,
“cause”: “not_group_by_or_distinct”
},
“analyzing_range_alternatives”: {
“range_scan_alternatives”: [
{
“index”: “report_product_sales_data_unique”,
“ranges”: [
“000030 <= hq_code <= 000030 AND 2018-05-11 < report_date”
],
“index_dives_for_eq_ranges”: true,
“rowid_ordered”: false,
“using_mrr”: false,
“index_only”: false,
“rows”: 1848962,
“cost”: 2.22e6,
“chosen”: true
},
{
“index”: “report_product_sales_data_hq_code_orgz_id_index”,
“ranges”: [
“000030 <= hq_code <= 000030 AND 229 <= orgz_id <= 229 AND 2018-05-11 < report_date”
],
“index_dives_for_eq_ranges”: true,
“rowid_ordered”: false,
“using_mrr”: false,
“index_only”: false,
“rows”: 37088,
“cost”: 44507,
“chosen”: true
}
],
“analyzing_roworder_intersect”: {
“usable”: false,
“cause”: “too_few_roworder_scans”
}
},
“chosen_range_access_summary”: {
“range_access_plan”: {
“type”: “range_scan”,
“index”: “report_product_sales_data_hq_code_orgz_id_index”,
“rows”: 37088,
“ranges”: [
“000030 <= hq_code <= 000030 AND 229 <= orgz_id <= 229 AND 2018-05-11 < report_date”
]
},
“rows_for_plan”: 37088,
“cost_for_plan”: 44507,
“chosen”: true
}
}
}
]
},
{
“considered_execution_plans”: [
{
“plan_prefix”: [
],
“table”: “`report_product_sales_data`”,
“best_access_path”: {
“considered_access_paths”: [
{
“access_type”: “ref”,
“index”: “report_product_sales_data_unique”,
“rows”: 1.85e6,
“cost”: 1.82e6,
“chosen”: true
},
{
// 可以看到选择 report_product_sales_data_hq_code_orgz_id_index 这个索引时 cost 最小
“access_type”: “ref”,
“index”: “report_product_sales_data_hq_code_orgz_id_index”,
“rows”: 37088,
“cost”: 44506,
“chosen”: true
},
{
“access_type”: “range”,
“rows”: 27816,
“cost”: 51924,
“chosen”: false
}
]
},
“cost_for_plan”: 44506,
“rows_for_plan”: 37088,
“chosen”: true
}
]
},
{
“attaching_conditions_to_tables”: {
“original_condition”: “((`report_product_sales_data`.`orgz_id` = 229) and (`report_product_sales_data`.`hq_code` = ‘000030’) and (`report_product_sales_data`.`product_id` in (11453,11472,11487,11446,11456,12088,11433,114170,11479,11491,11485,11482,70672,68998,154298,11435,11481,11515,122573,167938)) and (`report_product_sales_data`.`report_date` > ‘2018-05-11’))”,
“attached_conditions_computation”: [
{
“access_type_changed”: {
“table”: “`report_product_sales_data`”,
“index”: “report_product_sales_data_hq_code_orgz_id_index”,
“old_type”: “ref”,
“new_type”: “range”,
“cause”: “uses_more_keyparts”
}
}
],
“attached_conditions_summary”: [
{
“table”: “`report_product_sales_data`”,
“attached”: “((`report_product_sales_data`.`orgz_id` = 229) and (`report_product_sales_data`.`hq_code` = ‘000030’) and (`report_product_sales_data`.`product_id` in (11453,11472,11487,11446,11456,12088,11433,114170,11479,11491,11485,11482,70672,68998,154298,11435,11481,11515,122573,167938)) and (`report_product_sales_data`.`report_date` > ‘2018-05-11’))”
}
]
}
},
{
“clause_processing”: {
“clause”: “ORDER BY”,
“original_clause”: “`report_product_sales_data`.`id` desc”,
“items”: [
{
“item”: “`report_product_sales_data`.`id`”
}
],
“resulting_clause_is_simple”: true,
“resulting_clause”: “`report_product_sales_data`.`id` desc”
}
},
{
“refine_plan”: [
{
“table”: “`report_product_sales_data`”,
“pushed_index_condition”: “((`report_product_sales_data`.`orgz_id` = 229) and (`report_product_sales_data`.`hq_code` = ‘000030’) and (`report_product_sales_data`.`report_date` > ‘2018-05-11’))”,
“table_condition_attached”: “(`report_product_sales_data`.`product_id` in (11453,11472,11487,11446,11456,12088,11433,114170,11479,11491,11485,11482,70672,68998,154298,11435,11481,11515,122573,167938))”,
“access_type”: “range”
}
]
},
{
“reconsidering_access_paths_for_index_ordering”: {
// 到了 order by id 这边时，MySQL 改变了执行计划，选择了 PRIMARY 主键索引
“clause”: “ORDER BY”,
“index_order_summary”: {
“table”: “`report_product_sales_data`”,
“index_provides_order”: true,
“order_direction”: “desc”,
“disabled_pushed_condition_on_old_index”: true,
“index”: “PRIMARY”,
“plan_changed”: true,
“access_type”: “index_scan”
}
}
}
]
}
},
{
“join_execution”: {
“select#”: 1,
“steps”: [
]
}
}
]
}

现象及修改方案

通过现象可以看到 MySQL 在 order by 主键 id 时，limit 值的大小达到了某个临界值后，改变了执行计划，选择了主键索引，但不知道具体的规则究竟是怎样。
既然如此，就不用 order by id 这个 clause，改为 order by report_date，因为 id 和 report_date 的大小是正相关的，而且可以走到 report_product_sales_data_hq_code_orgz_id_index 索引，换了个法子解决了当前这个问题。

explain select product_id, sales_num, report_date from `report_product_sales_data`
where `hq_code` = ‘000030’
and `orgz_id` = 229
and `product_id` in (11453,11472,11487,11446,11456,12088,11433,114170,11479,11491,11485,11482,70672,68998,154298,11435,11481,11515,122573,167938)
and `report_date` > ‘2018-05-11’
order by `report_date` desc limit 10;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE report_product_sales_data range report_product_sales_data_unique,report_product_sales_data_hq_code_orgz_id_index report_product_sales_data_hq_code_orgz_id_index 55 NULL 37088 Using index condition; Using where

总结

在 order by id 的情况下，MySQL 由于自身的优化器选择，为了避免某些排序的消耗，可能会走非预期的 PRIMARY 主键索引；
order by 和 limit 结合使用，如果 where 字段，order by 字段都是索引，那么有 limit 索引会使用 order by 字段所在的索引，没有 limit 会使用 where 条件的索引；
对于数据量比较大，而且执行量很高的分页 sql，尽可能将所有的查询字段包括在索引中，同时使用索引来消除排序；
多用 explain 查看是否使用到了最优索引；
利用 optimizer trace 查看优化器执行过程；
观察 mysql 的 slow_query_log，及时做排查优化。

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