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The following content mainly brings you the details of the information provided by the information_ schema library. The knowledge mentioned here, which is slightly different from books, is summed up by professional and technical personnel in the process of contact with users, and has a certain value of experience sharing, hoping to bring help to the broad masses of readers.

Information_schema provides access to database metadata, statistics, and information about MySQL Server (for example, database or table names, data types and access permissions for fields, and so on). The information stored in the information_schema library can also be referred to as the MySQL data dictionary or system directory. This article is mainly about the field information of all tables in the information_schema library, which can be understood by interested friends.

After sql injection, the field information of all tables can be obtained through this database.

1.

COLLATIONS table

Provides information about the collation for each character set. The COLLATIONS table contains the following:

COLLATION_NAME collation name.

The name of the character set that the CHARACTER_SET_NAME is associated with the collation.

ID collation ID.

Whether the IS_DEFAULT collation is the default for its character set.

Whether the IS_COMPILED character set has been compiled into the CVM.

SORTLEN this is related to the amount of memory required to sort the strings represented in the character set.

two。

SHOW COLLATION;// can also query collation information

3.

COLLATION_CHARACTER_SET_APPLICABILITY table

COLLATION_NAME collation name.

The name of the character set that CHARACTER_SET_NAME is associated with the collation

4.

COLUMNS provides information about the fields in the table

TABLE_CATALOG contains the name of the directory to which the table of the column belongs. The value is always def.

TABLE_SCHEMA contains the name of the database where the field resides.

TABLE_NAME contains the name of the table in which the field resides.

The name of the COLUMN_NAME field.

The location of the fields in the ORDINAL_POSITION table. ORDINAL_POSITION is necessary because you may want to say ORDER BY ORDINAL_POSITION. Unlike SHOW COLUMNS, SELECT in the COLUMNS table does not have automatic sorting. The syntax of show columns is for example: show columns from my_test.user

Default value for the COLUMN_DEFAULT field. This value is NULL if the field has an explicit default value of NULL, or if the field definition does not contain a DEFAULT clause.

The IS_NULLABLE field can be null. If the null value can be stored in a column, the value is YES, otherwise it is NO.

DATA_TYPE field data type. The DATA_ type value is just the type name and has no other information.

The COLUMN_TYPE value contains the type name and other possible information, such as precision or length.

CHARACTER_MAXIMUM_LENGTH for string columns, the maximum length in characters.

CHARACTER_OCTET_LENGTH for string columns, the maximum length in bytes.

NUMERIC_PRECISION for numeric fields, numeric precision.

NUMERIC_SCALE for numeric fields, numeric scales.

DATETIME_PRECISION for time field, fractional second precision.

CHARACTER_SET_NAME for string fields, character set name.

COLLATION_NAME for string fields, collation name.

COLUMN_TYPE field data type.

The DATA_TYPE value is just the type name and has no other information.

The COLUMN_TYPE value contains the type name and other possible information, such as precision or length.

Whether the COLUMN_KEY name is indexed

EXTRA any other available information about a given field.

PRIVILEGES your permissions on this field.

Any comments contained in the COLUMN_COMMENT field definition.

GENERATION_EXPRESSION displays the expression used to calculate the column value for the generated field.

Related tutorials: mysql Video tutorial

These are the details of the field information of all tables in the [MySQL] information_schema library. For more information, please follow other related articles!

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