DBA技术分享-MySQL外键查询语句
一、术分概述
作为DBA分享几个工作中关于外键的外键常用查询。具体如下 ：
如何查询用户数据库（模式）中定义的查询外键约束。如何查询所有引用具有外键的语句特定的表。如何查询没有外键的术分表。如何查找没有关系的外键表 - Loner Tables。如何查询MySQL 数据库中没有关系表的查询比率。二、语句相关SQL1、术分查询用户数据库（模式）中定义的外键外键约束select concat(fks.constraint_schema, ., fks.table_name) as foreign_table,
-> as rel,
concat(fks.unique_constraint_schema, ., fks.referenced_table_name)
as primary_table,
fks.constraint_name,
group_concat(kcu.column_name
order by position_in_unique_constraint separator , )
as fk_columns
from information_schema.referential_constraints fks
join information_schema.key_column_usage kcu
on fks.constraint_schema = kcu.table_schema
and fks.table_name = kcu.table_name
and fks.constraint_name = kcu.constraint_name
-- where fks.constraint_schema = database name
group by fks.constraint_schema,
fks.table_name,
fks.unique_constraint_schema,
fks.referenced_table_name,
fks.constraint_name
order by fks.constraint_schema,
fks.table_name;注意：如果您需要特定数据库（模式）的信息，请取消注释 where 子句并提供您的查询数据库名称。
2、亿华云语句查询所有引用具有外键的术分特定的表。select distinct concat(table_schema,外键 ., table_name) as foreign_table,
>- as rel,
concat(referenced_table_schema, ., referenced_table_name)
as primary_table
from information_schema.key_column_usage
where referenced_table_name = table name -- provide table name here
-- and table_schema = database name
order by foreign_table;说明：
foreign_table - 外部表名 - 您要查找的表。rel - 涉及 FK 和方向的查询关系符号。primary_table - 主要（引用）表名 - 您作为参数提供的表。
select tab.table_schema as database_name,
tab.table_name,
>- no FKs as foreign_keys
from information_schema.tables tab
left join information_schema.table_constraints fks
on fks.table_schema = tab.table_schema
and fks.table_name = tab.table_name
and fks.constraint_type = FOREIGN KEY
where tab.table_type = BASE TABLE
and tab.table_schema not in (mysql, information_schema,
performance_schema, sys)
and fks.table_name is null
-- and tab.table_schema = your database name
order by tab.table_schema,
tab.table_name;说明：
database_name - 数据库的名称（模式）。table_name - 表的名称。foreign_keys - 表示缺少 FK 的符号。
select No FKs >- as refs,
concat(tab.table_schema, ., tab.table_name) as table,
>- no FKs as fks
from information_schema.tables tab
left join information_schema.referential_constraints ref
on tab.table_schema = ref.constraint_schema
and tab.table_name = ref.table_name
left join information_schema.referential_constraints ref_by
on tab.table_schema = ref_by.unique_constraint_schema
and tab.table_name = ref_by.referenced_table_name
where ref.constraint_name is null
and ref_by.constraint_name is null
and tab.table_type = BASE TABLE
and tab.table_schema not in (mysql, information_schema,
performance_schema, sys)
-- and tab.table_schema = your database name
order by tab.table_schema,
tab.table_name;说明：
refs - 表示缺少外键约束引用的图标。云服务器提供商table- 表的名称。fks - 象征缺少外键约束的图标。
select all_tables as table_count,
no_rel as loner_tables,
concat(cast(100.0*(no_rel/all_tables) as decimal(5,2)), %)
as loner_ratio
from
(select count(distinct concat(tab.table_schema, ., tab.table_name))
as all_tables,
SUM(case when ref.constraint_name is null
and ref_by.constraint_name is null
then 1
else 0 end) as no_rel
from information_schema.tables tab
left join information_schema.referential_constraints ref
on tab.table_schema = ref.constraint_schema
and tab.table_name = ref.table_name
left join information_schema.referential_constraints ref_by
on tab.table_schema = ref_by.unique_constraint_schema
and tab.table_name = ref_by.referenced_table_name
where tab.table_type = BASE TABLE
and tab.table_schema not in (mysql, information_schema,
sys, performance_schema)
) temp;说明：
table_count - 数据库中的表数（模式）。loner_tables - 数据库中Loner 表的数量（模式）。loner_ratio -孤独者比率- 数据库中孤独者表的百分比（模式）。
三、小结
mysql外键是我们工作中经常遇到的，这几个关于外键查询，可以帮忙提高数据库维护的效率。