In DynamoDB, tables, items, and attributes are the core components that you work with. A table is a collection of items, and each item is a collection of attributes. DynamoDB uses primary keys to uniquely identify each item in a table and secondary indexes to provide more querying flexibility. You can use DynamoDB Streams to capture data modification events in DynamoDB tables. Show There are limits in DynamoDB. For more information, see Service, account, and table quotas in Amazon DynamoDB. The following video will give you an introductory look at tables, items, and attributes. Tables, items, and attributes Tables, items, and attributesThe following are the basic DynamoDB components:
The following diagram shows a table named People with some example items and attributes. People { "PersonID": 101, "LastName": "Smith", "FirstName": "Fred", "Phone": "555-4321" } { "PersonID": 102, "LastName": "Jones", "FirstName": "Mary", "Address": { "Street": "123 Main", "City": "Anytown", "State": "OH", "ZIPCode": 12345 } } { "PersonID": 103, "LastName": "Stephens", "FirstName": "Howard", "Address": { "Street": "123 Main", "City": "London", "PostalCode": "ER3 5K8" }, "FavoriteColor": "Blue" }Note the following about the People table:
The following is another example table named Music that you could use to keep track of your music collection. Music { "Artist": "No One You Know", "SongTitle": "My Dog Spot", "AlbumTitle": "Hey Now", "Price": 1.98, "Genre": "Country", "CriticRating": 8.4 } { "Artist": "No One You Know", "SongTitle": "Somewhere Down The Road", "AlbumTitle": "Somewhat Famous", "Genre": "Country", "CriticRating": 8.4, "Year": 1984 } { "Artist": "The Acme Band", "SongTitle": "Still in Love", "AlbumTitle": "The Buck Starts Here", "Price": 2.47, "Genre": "Rock", "PromotionInfo": { "RadioStationsPlaying": { "KHCR", "KQBX", "WTNR", "WJJH" }, "TourDates": { "Seattle": "20150622", "Cleveland": "20150630" }, "Rotation": "Heavy" } } { "Artist": "The Acme Band", "SongTitle": "Look Out, World", "AlbumTitle": "The Buck Starts Here", "Price": 0.99, "Genre": "Rock" }Note the following about the Music table:
For more information, see Working with tables and data in DynamoDB. Primary keyWhen you create a table, in addition to the table name, you must specify the primary key of the table. The primary key uniquely identifies each item in the table, so that no two items can have the same key. DynamoDB supports two different kinds of primary keys:
The partition key of an item is also known as its hash attribute. The term hash attribute derives from the use of an internal hash function in DynamoDB that evenly distributes data items across partitions, based on their partition key values. The sort key of an item is also known as its range attribute. The term range attribute derives from the way DynamoDB stores items with the same partition key physically close together, in sorted order by the sort key value. Each primary key attribute must be a scalar (meaning that it can hold only a single value). The only data types allowed for primary key attributes are string, number, or binary. There are no such restrictions for other, non-key attributes. Secondary indexesYou can create one or more secondary indexes on a table. A secondary index lets you query the data in the table using an alternate key, in addition to queries against the primary key. DynamoDB doesn't require that you use indexes, but they give your applications more flexibility when querying your data. After you create a secondary index on a table, you can read data from the index in much the same way as you do from the table. DynamoDB supports two kinds of indexes:
Each table in DynamoDB has a quota of 20 global secondary indexes (default quota) and 5 local secondary indexes. In the example Music table shown previously, you can query data items by Artist (partition key) or by Artist and SongTitle (partition key and sort key). What if you also wanted to query the data by Genre and AlbumTitle? To do this, you could create an index on Genre and AlbumTitle, and then query the index in much the same way as you'd query the Music table. The following diagram shows the example Music table, with a new index called GenreAlbumTitle. In the index, Genre is the partition key and AlbumTitle is the sort key.
Note the following about the GenreAlbumTitle index:
You can query the GenreAlbumTitle index to find all albums of a particular genre (for example, all Rock albums). You can also query the index to find all albums within a particular genre that have certain album titles (for example, all Country albums with titles that start with the letter H). For more information, see Improving data access with secondary indexes. DynamoDB StreamsDynamoDB Streams is an optional feature that captures data modification events in DynamoDB tables. The data about these events appear in the stream in near-real time, and in the order that the events occurred. Each event is represented by a stream record. If you enable a stream on a table, DynamoDB Streams writes a stream record whenever one of the following events occurs:
Each stream record also contains the name of the table, the event timestamp, and other metadata. Stream records have a lifetime of 24 hours; after that, they are automatically removed from the stream. You can use DynamoDB Streams together with AWS Lambda to create a trigger—code that runs automatically whenever an event of interest appears in a stream. For example, consider a Customers table that contains customer information for a company. Suppose that you want to send a "welcome" email to each new customer. You could enable a stream on that table, and then associate the stream with a Lambda function. The Lambda function would run whenever a new stream record appears, but only process new items added to the Customers table. For any item that has an EmailAddress attribute, the Lambda function would invoke Amazon Simple Email Service (Amazon SES) to send an email to that address. In this example, the last customer, Craig Roe, will not receive an email because he doesn't have an EmailAddress. In addition to triggers, DynamoDB Streams enables powerful solutions such as data replication within and across AWS Regions, materialized views of data in DynamoDB tables, data analysis using Kinesis materialized views, and much more. For more information, see Change data capture for DynamoDB Streams. How do I sort multiple fields in Access query?To apply a multilevel sort:
Open the query and switch to Design view. Locate the field you want to sort first. In the Sort: row, click the drop-down arrow to select either an ascending or descending sort. Repeat the process in the other fields to add additional sorts.
What is a major sort key?A field or fields in a record that dictate the sequence of the file. For example, the sort keys STATE and NAME arrange the file alphabetically by name within state. STATE is the major sort key, and NAME is the minor key.
How do you sort a field by query in Access?To sort records:. Select a field you want to sort by. ... . Click the Home tab on the Ribbon, and locate the Sort & Filter group.. Sort the field by selecting the Ascending or Descending command.. The table will now be sorted by the selected field.. To save the new sort, click the Save command on the Quick Access Toolbar.. What are the two main sort orders in Access?You can sort both text and numbers in two ways: in ascending order and descending order. Ascending means going up, so an ascending sort will arrange numbers from smallest to largest and text from A to Z. Descending means going down, or largest to smallest for numbers and Z to A for text.
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