Simplified Query Language Syntax

Select Statements

Update and Delete Statements

Simplified Query Language Syntax

This section briefly describes the syntax of the query language so that youcan quickly move on to the next section,Example Queries. When you areready to learn about the syntax in more detail, see the sectionFull Query Language Syntax.

Select Statements

A select query has six clauses:SELECT,FROM,WHERE,GROUP BY,HAVING, andORDER BY. TheSELECT andFROM clauses are required, but theWHERE,GROUP BY,HAVING,andORDER BY clauses are optional. Here is the high-level BNF syntax of aquery language query:

QL_statement ::= select_clause from_clause   [where_clause][groupby_clause][having_clause][orderby_clause]

TheSELECT clause defines the types of the objects or values returned bythe query.

TheFROM clause defines the scope of the query by declaring one ormore identification variables, which can be referenced in theSELECT andWHERE clauses. Anidentification variable represents one of the following elements:

• The abstract schema name of an entity

• An element of a collection relationship

• An element of a single-valued relationship

• A member of a collection that is the multiple side of a one-to-many relationship

TheWHERE clause is a conditional expression that restricts the objects or valuesretrieved by the query. Although it is optional, most queries have aWHEREclause.

TheGROUP BY clause groups query results according to a set of properties.

TheHAVING clause is used with theGROUP BY clause to further restrict thequery results according to a conditional expression.

TheORDER BY clause sorts the objects or values returned by the query intoa specified order.

Update and Delete Statements

Update and delete statements provide bulk operations over sets of entities. They havethe following syntax:

update_statement :: = update_clause [where_clause] delete_statement :: =         delete_clause [where_clause]

The update and delete clauses determine the type of the entities to beupdated or deleted. TheWHERE clause may be used to restrict the scopeof the update or delete operation.

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