Query Specification

The query specification represents the result of a complex database query. The most common SELECT statements are just query specifications.

<query specification> ::= 
    SELECT ( DISTINCT | ALL )? 
        <select list> <from clause> 
          ( <where clause> )? ( <group by clause> )?
            ( <having clause> )?.

         

The result of a <query specification> is constructed as follows:

1. The <from clause> is evaluated.

2. If a <where clause> is specified, the result is filtered by applying the <search condition> of the <where clause> . The new result has the same degree as the previous result.

3. If a <group by clause> is specified, the specified grouping is performed on the result. The new result has the same degree as the previous result.

4. If a <having clause> is specified, the result is filtered by applying the <search condition> of the <having clause> . The new result has the same degree as the previous result.

5. The <value expression> s in the <select list> is calculated. The new result is a table that has the degree and the <display name> s of the <select list> .

6. If DISTINCT is specified, all duplicate rows from the result are filtered. Else the result remains unchanged. (Specifying ALL has no effect.)

DISTINCT may be specified only once in a <query specification> .