odps:tldr:38729

The command "desc ${table_name}" is used to describe the structure of a database table in SQL (Structured Query Language).

Here's how the command works:

• "desc" is short for "describe".
• "${table_name}" is a placeholder for the name of the table you want to describe. You need to replace it with the actual name of the table you want to get information about.

When you execute this command, it will provide information about the columns of the specified table, including the column names, data types, and any constraints or indexes defined on the columns.

The output of the command may vary depending on the database management system (DBMS) you are using, but it typically includes details such as:

• Column name: The name of the column in the table.
• Data type: The data type of the values stored in the column (e.g., integer, text, date).
• Nullable: Indicates whether the column allows NULL values or not.
• Default value: If a default value is specified for the column, it will be displayed.
• Constraints: If any constraints (like primary key, foreign key, unique) are defined on the column, they will be listed.

Overall, this command provides a quick way to gather information about the structure of a database table without writing a complex query or accessing metadata tables directly.