【MySQL】常用語句

一. 修改自增長字段值

1. 自增長起始值修改只能比原來更大，不能更小
2. alter table testid auto_increment=100;

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二. 事務

1. 隔離級別

查看事務隔離級別：show variables like 'transaction_isolation';
默認值：('transaction_isolation', 'REPEATABLE-READ');

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三. 數據統計

1. 數據庫表信息

select
table_schema as '數據庫',
table_name as '表名',
table_rows as '記錄數',
truncate(data_length/1024/1024, 2) as '數據容量(MB)',
truncate(index_length/1024/1024, 2) as '索引容量(MB)',
AUTO_INCREMENT as '自增長初始值',
ENGINE,
UPDATE_TIME,
TABLE_COMMENT
from information_schema.tables
where table_schema='庫名'
order by table_rows desc, index_length desc;

SELECT count(TABLE_NAME) FROM information_schema.TABLES WHERE TABLE_SCHEMA='庫名';

1. table_schema: 記錄數據庫名
2. table_name: 記錄數據表名
3. engine : 存儲引擎
4. table_rows: 關於表的粗略行估計
5. data_length : 記錄表的大小（單位字節）
6. index_length : 記錄表的索引的大小
7. row_format: 可以查看數據表是否壓縮過

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2. 列信息

SELECT * FROM information_schema.COLUMNS WHERE TABLE_SCHEMA = '數據庫名'
ORDER BY TABLE_NAME DESC ;

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3. 索引信息

SELECT * FROM information_schema.STATISTICS WHERE TABLE_SCHEMA = '數據庫名' and table_name='表名'
ORDER BY INDEX_NAME DESC,SEQ_IN_INDEX ;

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4. 事務

1. 執行時間超過1秒的事務語句

select * from information_schema.innodb_trx where TIME_TO_SEC(timediff(now(),trx_started)) > 1