TABLE_CONSTRAINTS
TABLE_CONSTRAINTS 表记录了表的约束信息。
USE information_schema;
DESC table_constraints;
+--------------------+--------------+------+------+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------------------+--------------+------+------+---------+-------+
| CONSTRAINT_CATALOG | varchar(512) | YES | | NULL | |
| CONSTRAINT_SCHEMA | varchar(64) | YES | | NULL | |
| CONSTRAINT_NAME | varchar(64) | YES | | NULL | |
| TABLE_SCHEMA | varchar(64) | YES | | NULL | |
| TABLE_NAME | varchar(64) | YES | | NULL | |
| CONSTRAINT_TYPE | varchar(64) | YES | | NULL | |
+--------------------+--------------+------+------+---------+-------+
6 rows in set (0.00 sec)
SELECT * FROM table_constraints WHERE constraint_type='UNIQUE';
+--------------------+--------------------+-------------------------+--------------------+-------------------------------------+-----------------+
| CONSTRAINT_CATALOG | CONSTRAINT_SCHEMA | CONSTRAINT_NAME | TABLE_SCHEMA | TABLE_NAME | CONSTRAINT_TYPE |
+--------------------+--------------------+-------------------------+--------------------+-------------------------------------+-----------------+
| def | mysql | name | mysql | help_topic | UNIQUE |
| def | mysql | tbl | mysql | stats_meta | UNIQUE |
| def | mysql | tbl | mysql | stats_histograms | UNIQUE |
| def | mysql | tbl | mysql | stats_buckets | UNIQUE |
| def | mysql | delete_range_index | mysql | gc_delete_range | UNIQUE |
| def | mysql | delete_range_done_index | mysql | gc_delete_range_done | UNIQUE |
| def | PERFORMANCE_SCHEMA | SCHEMA_NAME | PERFORMANCE_SCHEMA | events_statements_summary_by_digest | UNIQUE |
+--------------------+--------------------+-------------------------+--------------------+-------------------------------------+-----------------+
7 rows in set (0.01 sec)
TABLE_CONSTRAINTS 表中列的含义如下：
CONSTRAINT_CATALOG：约束所属的目录的名称。这个值总是def。CONSTRAINT_SCHEMA：约束所属的数据库的名称。CONSTRAINT_NAME：约束的名称。TABLE_NAME：表的名称。CONSTRAINT_TYPE：约束的类型。取值可以是UNIQUE、PRIMARY KEY或者FOREIGN KEY。UNIQUE和PRIMARY KEY信息与SHOW INDEX语句的执行结果类似。