EXPLAIN EXTENDED

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EXPLAIN  EXTENDED 
SELECT
  *
FROM
  `receivable_application_relation` d
WHERE d.`application_id` IN
  (SELECT
    id
  FROM
    application
  WHERE application_code IN (
      'ZYHT20190305192721001',
      'ZYHT20190309152839001',
      'ZYHT20190309152904001'
    ));

SHOW WARNINGS;

查看优化后最终执行的sql

In 并不是走的子查询而是 join ，这个是从上面的画红线的地方copy 出来的

SELECT
  `cf_receivables_financing`.`d`.`id` AS `id`,
  `cf_receivables_financing`.`d`.`application_id` AS `application_id`,
  `cf_receivables_financing`.`d`.`receivable_id` AS `receivable_id`,
  `cf_receivables_financing`.`d`.`update_time` AS `update_time`,
  `cf_receivables_financing`.`d`.`create_time` AS `create_time`,
  `cf_receivables_financing`.`d`.`deleted` AS `deleted`
FROM
  `cf_receivables_financing`.`application`
  JOIN `cf_receivables_financing`.`receivable_application_relation` `d`
WHERE (
    (
      `cf_receivables_financing`.`d`.`application_id` = `cf_receivables_financing`.`application`.`id`
    )
    AND (
      `cf_receivables_financing`.`application`.`application_code` IN (
        'ZYHT20190305192721001',
        'ZYHT20190309152839001',
        'ZYHT20190309152904001'
      )
    )
  )

EXPLAIN EXTENDED 
SELECT
d.*
FROM
`receivable_application_relation` d
INNER JOIN application a
ON d.`application_id` = a.id
WHERE a.application_code IN (
'ZYHT20190305192721001',
'ZYHT20190309152839001',
'ZYHT20190309152904001'
);

查看优化后的sql

SELECT
  `cf_receivables_financing`.`d`.`id` AS `id`,
  `cf_receivables_financing`.`d`.`application_id` AS `application_id`,
  `cf_receivables_financing`.`d`.`receivable_id` AS `receivable_id`,
  `cf_receivables_financing`.`d`.`update_time` AS `update_time`,
  `cf_receivables_financing`.`d`.`create_time` AS `create_time`,
  `cf_receivables_financing`.`d`.`deleted` AS `deleted`
FROM
  `cf_receivables_financing`.`receivable_application_relation` `d`
  JOIN `cf_receivables_financing`.`application` `a`
WHERE (
    (
      `cf_receivables_financing`.`d`.`application_id` = `cf_receivables_financing`.`a`.`id`
    )
    AND (
      `cf_receivables_financing`.`a`.`application_code` IN (
        'ZYHT20190305192721001',
        'ZYHT20190309152839001',
        'ZYHT20190309152904001'
      )
    )
  );

原文地址：https://www.cnblogs.com/fanBlog/p/11943748.html

Mysql查看优化后的SQL 语句

EXPLAIN EXTENDED

SHOW WARNINGS;