RDH: Creating an SQL query from a DAP2 Constraint Expression: Difference between revisions
From OPeNDAP Documentation
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would be converted in the SQL query: | would be converted in the SQL query: | ||
SELECT v, u FROM foo WHERE lat<26 AND lat>24 AND lon<-126 AND lon>-128 | SELECT v, u FROM foo WHERE lat<26 AND lat>24 AND lon<-126 AND lon>-128 | ||
Additionally we may wish to add: | |||
# The use of a limited regular expression type of matching in the CE which could be used to create [http://www.w3schools.com/sql/sql_like.asp SQL "LIKE" operators]. | |||
# Some kind of a range operation that would map to [http://www.w3schools.com/sql/sql_between.asp SQL "BETWEEN" operator]. | |||
== Server Side Functions == | == Server Side Functions == | ||
Additionally we may wish to add: | Additionally we may wish to add: | ||
# A server side function that allows the user to specify that they only wish to receive ''unique'' (aka ''distinct'') values in the response. This would utilize the [http://www.w3schools.com/sql/sql_distinct.asp SQL "DISTINCT" operator]. | # A server side function that allows the user to specify that they only wish to receive ''unique'' (aka ''distinct'') values in the response. This would utilize the [http://www.w3schools.com/sql/sql_distinct.asp SQL "DISTINCT" operator]. | ||
Revision as of 17:19, 5 May 2009
DAP Projection
- Each projected variable should appear as selected columns in the SQL SELECT statement.
- The name of the Data Source (which is the DAP resource ID) should be used in the FROM section of the SELECT statement.
DAP Selection
- Each clause should be converted (where possible) into a condition in the SQL SELECT statements WHERE clause.
- Array sub-setting cannot be encoded in the SQL query and must happen once the row set response has been received.
For example, the request:
http://localhost/opendap/rdh/foo?v,u&lat<26&lat>24&lon<-126&lon>-128
would be converted in the SQL query:
SELECT v, u FROM foo WHERE lat<26 AND lat>24 AND lon<-126 AND lon>-128
Additionally we may wish to add:
- The use of a limited regular expression type of matching in the CE which could be used to create SQL "LIKE" operators.
- Some kind of a range operation that would map to SQL "BETWEEN" operator.
Server Side Functions
Additionally we may wish to add:
- A server side function that allows the user to specify that they only wish to receive unique (aka distinct) values in the response. This would utilize the SQL "DISTINCT" operator.
