The SimpleDB Select API uses a query language that is similar to the SQL Select statementThis query language makes SimpleDB Selects very approachable with a gentle learning curve Keep in mind, however, that SimpleDB applies the familiar SQL terminology to domains and attributes rather than tables and columnsThese structures are analogous but not identicalAlso, be aware that there are no relations, joins, or sub-selects Select But Not DELETE

The presence of an API roughly based on SQL Select statements might lead you to wonder if there are also other SQL statements available, such as INSERT, UPDATE, or DELETE The answer is no; these other SQL statements do not exist in the SimpleDB API All data, whether new or updated, is stored via calls to PutAttributes

Notably, the bulk deletion capabilities of the SQL DELETE statement are absent Data can be stored or retrieved in batches, but items must be deleted one at a timeAWS has a good record for responding to customer feedback, so if this becomes a highly requested feature, it could be the target of a future enhancement

The minimal Select statement consists of two required clauses an output selection clause followed by a domain clause:

The output selection clause begins with SELECT and is followed by a specification of what output is requestedThe domain clause begins with the keyword FROM, and because there are no joins in SimpleDB, ends with the case-sensitive name of a single domain to be queriedThe domain name is subject to the Select quoting rule for names Select Keywords

Keywords in the SimpleDB Select query language will be uppercase in the examples in this book for clarity However, they are not case sensitive You can use lowercase in your own Select statements A complete list of the Select keywords follow: SELECT FROM WHERE LIKE INTERSECTION OR IN BETWEEN AND EVERY IS NOT NULL ORDER BY DESC ASC LIMIT

In addition, lowercase is used for all of the example domain names and attribute names to easily distinguish between user-defined names and query language keywords

Domain names and attribute names can appear in various places within a Select expression Depending on the characters used in a name, it may need to be quotedThe character used for quoting names is the backtick (`) Quoting is optional if the name contains only letters, numbers, dollar signs, and underscores and does not start with a number In all other cases, the name must be quoted with backtick characters

If the name itself contains the backtick character, it must be escaped when used in a Select expression Substitute each backtick with two backtick characters For example, the attribute name cats`dogs becomes `cats``dogs` when quoted and escaped according to this rule Note

SimpleDB imposes much stricter naming requirements on domain names than on attribute names Because of the restricted set of characters, quoting is less frequently an issue for domain names The only characters allowed in a domain name that trigger the name quoting rule are the dot (), the hyphen (-), and a leading number

The initial clause of the Select expression lists the data to be returned for matching resultsThere are three ways to specify the output, all beginning with the SELECT keyword, as follows:

Use an asterisk to request all attributes:

Use a function to request the count:

List the attribute names specifically:

The size of an explicit attribute list can be from 1 to 256A comma is used to separate attribute names when more than one is given Each attribute name in this list is subject to the Select quoting rule for names (as discussed previously)You can also request the item name by including the function itemName() in the list: