Question

我有一个超过870.000行的数据库。每次收到请求时，我都必须执行COUNT来检查是否存在行。这些COUNT个请求在执行前最多需要180秒。这很长。

这是我的疑问：

SELECT COUNT(0) AS aantal FROM milk_quotes WHERE shopId = '438' AND quoteId = '17424765'

EXPLAIN EXTENDED显示：

id  select_type table   type    possible_keys   key key_len ref rows    filtered    Extra
1   SIMPLE  milk_quotes ref shopId  shopId  4   const   87648   100.00  Using where

表结构是：

CREATE TABLE `milk_quotes ` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `shopId` mediumint(11) DEFAULT NULL,
  `quoteId` bigint(11) DEFAULT NULL,
  `customerId` bigint(11) DEFAULT NULL,
  `customerIP` int(11) unsigned DEFAULT NULL,
  `recoveryHash` char(32) CHARACTER SET latin1 DEFAULT NULL,
  `language` varchar(2) CHARACTER SET latin1 DEFAULT 'nl',
  `channel` varchar(11) CHARACTER SET latin1 DEFAULT NULL,
  `productsCount` int(11) DEFAULT NULL,
  `isPaid` tinyint(1) DEFAULT '0',
  `isNotified` enum('0','1') CHARACTER SET latin1 DEFAULT '0',
  `paymentId` varchar(50) CHARACTER SET latin1 DEFAULT NULL,
  `paymentCountry` varchar(2) CHARACTER SET latin1 DEFAULT NULL,
  `priceIncl` decimal(10,2) DEFAULT NULL,
  `createdAt` timestamp NULL DEFAULT CURRENT_TIMESTAMP,
  `updatedAt` timestamp NULL DEFAULT NULL,
  `shopUpdatedAt` timestamp NULL DEFAULT NULL,
  `recalculatedAt` timestamp NULL DEFAULT NULL,
  `shopCreatedAt` timestamp NULL DEFAULT NULL,
  `firstReminder` mediumint(9) DEFAULT NULL,
  `secondReminder` mediumint(9) DEFAULT NULL,
  `thirdReminder` mediumint(9) DEFAULT NULL,
  `skipQuote` enum('1','0') DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `isPaid` (`isPaid`),
  KEY `shopId` (`shopId`),
  KEY `firstReminder` (`firstReminder`)
) ENGINE=InnoDB AUTO_INCREMENT=930952 DEFAULT CHARSET=utf8;

Inno DB变量：

have_innodb YES
ignore_builtin_innodb   OFF
innodb_adaptive_hash_index  ON
innodb_additional_mem_pool_size 1048576
innodb_autoextend_increment 8
innodb_autoinc_lock_mode    1
innodb_buffer_pool_size 8388608
innodb_checksums    ON
innodb_commit_concurrency   0
innodb_concurrency_tickets  500
innodb_data_file_path   ibdata1:10M:autoextend
innodb_data_home_dir    
innodb_doublewrite  ON
innodb_fast_shutdown    1
innodb_file_io_threads  4
innodb_file_per_table   OFF
innodb_flush_log_at_trx_commit  1
innodb_flush_method 
innodb_force_recovery   0
innodb_lock_wait_timeout    50
innodb_locks_unsafe_for_binlog  OFF
innodb_log_buffer_size  1048576
innodb_log_file_size    5242880
innodb_log_files_in_group   2
innodb_log_group_home_dir   ./
innodb_max_dirty_pages_pct  90
innodb_max_purge_lag    0
innodb_mirrored_log_groups  1
innodb_open_files   300
innodb_rollback_on_timeout  OFF
innodb_stats_on_metadata    ON
innodb_support_xa   ON
innodb_sync_spin_loops  20
innodb_table_locks  ON
innodb_thread_concurrency   8
innodb_thread_sleep_delay   10000
innodb_use_legacy_cardinality_algorithm ON

Answer 1

查询在每个查询中每个表只能使用一个索引;因此，如果要在单个查询中查找多个字段，则需要有一个涵盖所有字段的索引。在您的查询中，使用shopId索引，但在quoteId内依次扫描，这不是很好（我假设每个商店有一堆quoteId行，是吗？）。尝试将架构中的shopId索引更改为

KEY `shopAndQuoteIds` (`shopId`, `quoteId`),

（如果你想在现有的表上执行它，我相信ALTER TABLE aantal DROP INDEX shopId后跟ALTER TABLE aantal ADD KEY shopAndQuoteIds (shopId, quoteId)应该这样做。在执行此操作之前备份你的数据库！或者，你可以转储表，将模式更改为上述模式，然后重新导入。）

请注意，可以使用密钥的任何前缀;因此(shopId, quoteId)索引可用于shopId查询和shopId + quoteId查询，但不能用于quoteId查询。事实上，它仍可用于普通shopId查询，这意味着您可以通过创建此新索引并删除旧的shopId来丢失任何内容。

MySQL简单COUNT需要很长时间

1 个答案: