Mysql/Maria唯一密钥表示_Mysql_Sql_Mariadb

Mysql/Maria唯一密钥表示

mysql sql mariadb

Mysql/Maria唯一密钥表示,mysql,sql,mariadb,Mysql,Sql,Mariadb,我想知道如何将密钥存储在mysql/mariadb数据库中。据我所知，information_schema.columns中存储了一些类型：PRI、MUL和UNI，分别表示主键、键和唯一键但事实并非如此 MariaDB [test]> CREATE TABLE test_table(leftkey int unsigned, rightkey int unsigned, unique key(leftkey, rightkey)); MariaDB [test]> DESC t

我想知道如何将密钥存储在mysql/mariadb数据库中。据我所知，information_schema.columns中存储了一些类型：PRI、MUL和UNI，分别表示主键、键和唯一键

但事实并非如此

MariaDB [test]> CREATE TABLE test_table(leftkey int unsigned, rightkey int unsigned, unique key(leftkey, rightkey));

MariaDB [test]> DESC test_table;
+----------+------------------+------+-----+---------+-------+
| Field    | Type             | Null | Key | Default | Extra |
+----------+------------------+------+-----+---------+-------+
| leftkey  | int(10) unsigned | YES  | MUL | NULL    |       |
| rightkey | int(10) unsigned | YES  |     | NULL    |       |
+----------+------------------+------+-----+---------+-------+

所以我有两个问题：

1如何检测密钥类型是唯一的？descripe命令显示类型为MUL，而不是UNI，表示简单键

2示例中的密钥对存储在何处：leftkey和rightkey？

不用麻烦描述，因为正如您所发现的，在某些情况下，它会给出不明确的信息

只需使用showcreatetable。这将准确地显示将重新创建表的SQL语法。然后您就可以确切地知道存在哪些键以及键的类型

mysql> show create table test_table\G
*************************** 1. row ***************************
       Table: test_table
Create Table: CREATE TABLE `test_table` (
  `leftkey` int(10) unsigned DEFAULT NULL,
  `rightkey` int(10) unsigned DEFAULT NULL,
  UNIQUE KEY `leftkey` (`leftkey`,`rightkey`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1

您还可以查询信息\u SCHEMA.STATISTICS以获得更精确的信息

mysql> select * from information_schema.statistics where table_name='test_table'\G
*************************** 1. row ***************************
TABLE_CATALOG: def
 TABLE_SCHEMA: test
   TABLE_NAME: test_table
   NON_UNIQUE: 0
 INDEX_SCHEMA: test
   INDEX_NAME: leftkey
 SEQ_IN_INDEX: 1
  COLUMN_NAME: leftkey
    COLLATION: A
  CARDINALITY: 0
     SUB_PART: NULL
       PACKED: NULL
     NULLABLE: YES
   INDEX_TYPE: BTREE
      COMMENT: 
INDEX_COMMENT: 
*************************** 2. row ***************************
TABLE_CATALOG: def
 TABLE_SCHEMA: test
   TABLE_NAME: test_table
   NON_UNIQUE: 0
 INDEX_SCHEMA: test
   INDEX_NAME: leftkey
 SEQ_IN_INDEX: 2
  COLUMN_NAME: rightkey
    COLLATION: A
  CARDINALITY: 0
     SUB_PART: NULL
       PACKED: NULL
     NULLABLE: YES
   INDEX_TYPE: BTREE
      COMMENT: 
INDEX_COMMENT:

或者信息\u SCHEMA.KEY\u列\u用法表的信息稍有不同：

mysql> select * from information_schema.key_column_usage where table_name = 'test_table'\G
*************************** 1. row ***************************
           CONSTRAINT_CATALOG: def
            CONSTRAINT_SCHEMA: test
              CONSTRAINT_NAME: leftkey
                TABLE_CATALOG: def
                 TABLE_SCHEMA: test
                   TABLE_NAME: test_table
                  COLUMN_NAME: leftkey
             ORDINAL_POSITION: 1
POSITION_IN_UNIQUE_CONSTRAINT: NULL
      REFERENCED_TABLE_SCHEMA: NULL
        REFERENCED_TABLE_NAME: NULL
       REFERENCED_COLUMN_NAME: NULL
*************************** 2. row ***************************
           CONSTRAINT_CATALOG: def
            CONSTRAINT_SCHEMA: test
              CONSTRAINT_NAME: leftkey
                TABLE_CATALOG: def
                 TABLE_SCHEMA: test
                   TABLE_NAME: test_table
                  COLUMN_NAME: rightkey
             ORDINAL_POSITION: 2
POSITION_IN_UNIQUE_CONSTRAINT: NULL
      REFERENCED_TABLE_SCHEMA: NULL
        REFERENCED_TABLE_NAME: NULL
       REFERENCED_COLUMN_NAME: NULL

不要费心去描述，因为正如你所发现的，它在某些情况下给出了模棱两可的信息

只需使用showcreatetable。这将准确地显示将重新创建表的SQL语法。然后您就可以确切地知道存在哪些键以及键的类型

mysql> show create table test_table\G
*************************** 1. row ***************************
       Table: test_table
Create Table: CREATE TABLE `test_table` (
  `leftkey` int(10) unsigned DEFAULT NULL,
  `rightkey` int(10) unsigned DEFAULT NULL,
  UNIQUE KEY `leftkey` (`leftkey`,`rightkey`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1

您还可以查询信息\u SCHEMA.STATISTICS以获得更精确的信息

mysql> select * from information_schema.statistics where table_name='test_table'\G
*************************** 1. row ***************************
TABLE_CATALOG: def
 TABLE_SCHEMA: test
   TABLE_NAME: test_table
   NON_UNIQUE: 0
 INDEX_SCHEMA: test
   INDEX_NAME: leftkey
 SEQ_IN_INDEX: 1
  COLUMN_NAME: leftkey
    COLLATION: A
  CARDINALITY: 0
     SUB_PART: NULL
       PACKED: NULL
     NULLABLE: YES
   INDEX_TYPE: BTREE
      COMMENT: 
INDEX_COMMENT: 
*************************** 2. row ***************************
TABLE_CATALOG: def
 TABLE_SCHEMA: test
   TABLE_NAME: test_table
   NON_UNIQUE: 0
 INDEX_SCHEMA: test
   INDEX_NAME: leftkey
 SEQ_IN_INDEX: 2
  COLUMN_NAME: rightkey
    COLLATION: A
  CARDINALITY: 0
     SUB_PART: NULL
       PACKED: NULL
     NULLABLE: YES
   INDEX_TYPE: BTREE
      COMMENT: 
INDEX_COMMENT:

或者信息\u SCHEMA.KEY\u列\u用法表的信息稍有不同：

mysql> select * from information_schema.key_column_usage where table_name = 'test_table'\G
*************************** 1. row ***************************
           CONSTRAINT_CATALOG: def
            CONSTRAINT_SCHEMA: test
              CONSTRAINT_NAME: leftkey
                TABLE_CATALOG: def
                 TABLE_SCHEMA: test
                   TABLE_NAME: test_table
                  COLUMN_NAME: leftkey
             ORDINAL_POSITION: 1
POSITION_IN_UNIQUE_CONSTRAINT: NULL
      REFERENCED_TABLE_SCHEMA: NULL
        REFERENCED_TABLE_NAME: NULL
       REFERENCED_COLUMN_NAME: NULL
*************************** 2. row ***************************
           CONSTRAINT_CATALOG: def
            CONSTRAINT_SCHEMA: test
              CONSTRAINT_NAME: leftkey
                TABLE_CATALOG: def
                 TABLE_SCHEMA: test
                   TABLE_NAME: test_table
                  COLUMN_NAME: rightkey
             ORDINAL_POSITION: 2
POSITION_IN_UNIQUE_CONSTRAINT: NULL
      REFERENCED_TABLE_SCHEMA: NULL
        REFERENCED_TABLE_NAME: NULL
       REFERENCED_COLUMN_NAME: NULL

信息_schema.columns描述作为约束的列而不是键。列在约束中使用，因此您需要使用一些其他信息\u架构表来获取信息

mysql> select * from information_schema.statistics where table_name='test_table'\G
*************************** 1. row ***************************
TABLE_CATALOG: def
 TABLE_SCHEMA: test
   TABLE_NAME: test_table
   NON_UNIQUE: 0
 INDEX_SCHEMA: test
   INDEX_NAME: leftkey
 SEQ_IN_INDEX: 1
  COLUMN_NAME: leftkey
    COLLATION: A
  CARDINALITY: 0
     SUB_PART: NULL
       PACKED: NULL
     NULLABLE: YES
   INDEX_TYPE: BTREE
      COMMENT: 
INDEX_COMMENT: 
*************************** 2. row ***************************
TABLE_CATALOG: def
 TABLE_SCHEMA: test
   TABLE_NAME: test_table
   NON_UNIQUE: 0
 INDEX_SCHEMA: test
   INDEX_NAME: leftkey
 SEQ_IN_INDEX: 2
  COLUMN_NAME: rightkey
    COLLATION: A
  CARDINALITY: 0
     SUB_PART: NULL
       PACKED: NULL
     NULLABLE: YES
   INDEX_TYPE: BTREE
      COMMENT: 
INDEX_COMMENT:

您可以使用以下查询获取有关约束的更多信息：

SELECT *
FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS TC
INNER JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE TK
 ON TC.CONSTRAINT_SCHEMA = TK.CONSTRAINT_SCHEMA
 AND TC.TABLE_SCHEMA = TK.TABLE_SCHEMA
 AND TC.TABLE_NAME   = TK.TABLE_NAME
 AND TC.CONSTRAINT_NAME = TK.CONSTRAINT_NAME

信息_schema.columns描述作为约束的列而不是键。列在约束中使用，因此您需要使用一些其他信息\u架构表来获取信息

mysql> select * from information_schema.statistics where table_name='test_table'\G
*************************** 1. row ***************************
TABLE_CATALOG: def
 TABLE_SCHEMA: test
   TABLE_NAME: test_table
   NON_UNIQUE: 0
 INDEX_SCHEMA: test
   INDEX_NAME: leftkey
 SEQ_IN_INDEX: 1
  COLUMN_NAME: leftkey
    COLLATION: A
  CARDINALITY: 0
     SUB_PART: NULL
       PACKED: NULL
     NULLABLE: YES
   INDEX_TYPE: BTREE
      COMMENT: 
INDEX_COMMENT: 
*************************** 2. row ***************************
TABLE_CATALOG: def
 TABLE_SCHEMA: test
   TABLE_NAME: test_table
   NON_UNIQUE: 0
 INDEX_SCHEMA: test
   INDEX_NAME: leftkey
 SEQ_IN_INDEX: 2
  COLUMN_NAME: rightkey
    COLLATION: A
  CARDINALITY: 0
     SUB_PART: NULL
       PACKED: NULL
     NULLABLE: YES
   INDEX_TYPE: BTREE
      COMMENT: 
INDEX_COMMENT:

您可以使用以下查询获取有关约束的更多信息：

SELECT *
FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS TC
INNER JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE TK
 ON TC.CONSTRAINT_SCHEMA = TK.CONSTRAINT_SCHEMA
 AND TC.TABLE_SCHEMA = TK.TABLE_SCHEMA
 AND TC.TABLE_NAME   = TK.TABLE_NAME
 AND TC.CONSTRAINT_NAME = TK.CONSTRAINT_NAME