檢視指定資料庫所佔空間

select concat(round(sum(data_length / 1024 / 1024), 2), 'MB') as data
  from information_schema.tables
 where table_schema = 'dbName';

檢視指定表所佔空間

select concat(round(sum(data_length / 1024 / 1024), 2), 'MB') as data
  from information_schema.tables
 where table_schema = 'dbName'
   and table_name = 'tableName';

檢視指定資料庫下各個表分別佔用的空間

select concat(round(sum(data_length / 1024 / 1024), 2), 'MB') as data,
       table_name
  from information_schema.tables
 where table_schema = 'dbName'
 GROUP BY table_name
 ORDER BY data desc;

檢視所有資料庫各自的容量大小

select table_schema as '資料庫名稱',
       sum(table_rows) as '記錄數',
       sum(truncate(data_length / 1024 / 1024, 2)) as '資料容量(MB)',
       sum(truncate(index_length / 1024 / 1024, 2)) as '索引容量(MB)'
  from information_schema.tables
 group by table_schema
 order by sum(data_length) desc, sum(index_length) desc;

檢視所有資料庫各表容量大小

select table_schema as '資料庫名稱',
       table_name as '表名',
       table_rows as '記錄數',
       truncate(data_length / 1024 / 1024, 2) as '資料容量(MB)',
       truncate(index_length / 1024 / 1024, 2) as '索引容量(MB)'
  from information_schema.tables
 order by data_length desc, index_length desc;

查看錶的碎片

select table_schema db_name,
       table_name,
       round(data_length / 1024 / 1024) as data_length_mb,
       round(index_length / 1024 / 1024) as index_length_mb,
       round(data_free / 1024 / 1024) as data_free_mb,
       engine
  from information_schema.tables
 where table_schema not in ('information_schema', 'mysql')
   and data_free > 0
 order by data_free_mb desc;

其中：

·data_length：對於innodb表，表示實際分配給聚簇索引的空間大小

·index_length：對於innodb表，表示實際分配給二級索引的空間大小

·data_free：對於innodb表，表示未使用的空間。對於分割槽表，這個值可能不準，具體要檢視information_schema.partitions

清除表碎片

方法1 alter table 表名 engine=InnoDB

alter table tableName engine=InnoDB;

方法2 optimize table 表名

#單個表
optimize table tableName;
#多個表
optimize table tableName1,tableName2,tableName3,tableName4;

方法3：

#針對單個表
mysqlcheck -o dbName1 tableName1 -u root -pxxxx

#針對某個庫
mysqlcheck -o dbName1 -u root -pxxxx

#針對所有的庫
mysqlcheck -o --all-databases -u root -pxxxx