Differences between getting table information from a relational (SQL) database and DynamoDB

You can verify that a table has been created according to your specifications. In a relational database, all of the table's schema is shown. Amazon DynamoDB tables are schemaless, so only the primary key attributes are shown.

Getting information about a table with SQL

Most relational database management systems (RDBMS) allow you to describe a table's structure—columns, data types, primary key definition, and so on. There is no standard way to do this in SQL. However, many database systems provide a DESCRIBE command. The following is an example from MySQL.

DESCRIBE Music;

This returns the structure of your table, with all of the column names, data types, and sizes.

+------------+-------------+------+-----+---------+-------+
| Field      | Type        | Null | Key | Default | Extra |
+------------+-------------+------+-----+---------+-------+
| Artist     | varchar(20) | NO   | PRI | NULL    |       |
| SongTitle  | varchar(30) | NO   | PRI | NULL    |       |
| AlbumTitle | varchar(25) | YES  |     | NULL    |       |
| Year       | int(11)     | YES  |     | NULL    |       |
| Price      | float       | YES  |     | NULL    |       |
| Genre      | varchar(10) | YES  |     | NULL    |       |
| Tags       | text        | YES  |     | NULL    |       |
+------------+-------------+------+-----+---------+-------+

The primary key for this table consists of Artist and SongTitle.

Getting information about a table in DynamoDB

DynamoDB has a DescribeTable operation, which is similar. The only parameter is the table name.

{
    TableName : "Music"
}

The reply from DescribeTable looks like the following.

{
  "Table": {
    "AttributeDefinitions": [
      {
        "AttributeName": "Artist",
        "AttributeType": "S"
      },
      {
        "AttributeName": "SongTitle",
        "AttributeType": "S"
      }
    ],
    "TableName": "Music",
    "KeySchema": [
      {
        "AttributeName": "Artist",
        "KeyType": "HASH"  //Partition key
      },
      {
        "AttributeName": "SongTitle",
        "KeyType": "RANGE"  //Sort key
      }
    ],

    ...

DescribeTable also returns information about indexes on the table, provisioned throughput settings, an approximate item count, and other metadata.