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SELECT (View)

Get a record from the specified view. The fields to get have to be already in the view. It produces one or zero static record and costs little time.

Synopsis

SELECT <* | column_name [AS field_alias] [, ...]>
  FROM view_name
  WHERE column_name = constant;

Notes

Selecting from a view is a very fast operation that takes advantage of the concept of a view. So it has a more restricted syntax than selecting from a stream:

  • The most important difference between SELECT from a stream and from a view is that the former has an EMIT CHANGES clause and the latter does not.
  • SELECT clause can only contain * or column names with/without aliases. Other ones such as constants, arithmetical expressions, aggregate/scalar functions, etc. are not allowed. And the column names should be in the SELECT clause of the query when creating the corresponding view.
  • FROM clause can only contain ONE view name. Clauses such as JOIN are not allowed.
  • WHERE clause can only contain ONE conditional expression in the form of column_name = constant. And the column_name has to be the same as which in the GROUP BY clause when creating the corresponding view and the constant has to be a literal whose value is known at compile time, see constant.

Examples

// Assume that this query has been executed successfully before
// CREATE VIEW my_view AS SELECT a, b, SUM(a), COUNT(*) AS cnt FROM foo GROUP BY b EMIT CHANGES;

SELECT `SUM(a)`, cnt, a FROM my_view WHERE b = 1;
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