1.7 Examples
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  • Documentation
    • Reference manual
    • Packages
      • Constraint Query Language A high level interface to SQL databases
        • library(cql/cql): CQL - Constraint Query Language
          • Examples
            • Simple INSERT
            • Simple INSERT with retrieval of identity of the inserted
            • Simple DELETE
            • Simple SELECT
            • Simple UPDATE
            • WHERE with arithmetic comparison
            • Simple INNER JOIN
            • Arithmetic UPDATE with an INNER JOIN and a WHERE restriction
            • Confirm row does not exist
            • Aggregation - Count
            • Aggregation - Sum
            • Aggregation - Average
            • Maximum Value
            • Minimum Value
            • Aggregation requiring GROUP BY
            • INNER JOIN with an aggregation sub-query where the sub-query is constrained by a shared variable from the main query
            • INNER JOIN in an aggregation sub-query
            • Negation
            • EXISTS
            • Left Outer Join
            • List-based Restrictions
            • Compile time in-list constraint
            • Disjunction resulting in OR in WHERE clause
            • Disjunction resulting in different joins (implemented as a SQL UNION)
            • Disjunction resulting in different SELECT attributes (implemented as separate ODBC queries)
            • ORDER BY
            • DISTINCT
            • SELECT with NOT NULL restriction
            • First N
            • Self JOIN
            • Removing null comparisions
            • Three table JOIN
            • Three table JOIN with NOLOCK locking hint
            • SELECT with LIKE
            • Writing exceptions directly to the database
            • TOP N is Parametric
            • Using compile_time_goal/1
            • ON
            • Expressions In Where Restrictions
            • Explicitly avoid the "No WHERE restriction" message
            • HAVING
            • INSERT and UPDATE value in-line formatting
            • Negations in WHERE Clauses
            • Predicate-generated Attribute Values
            • INSERT from SELECT

1.7.22 Compile time in-list constraint

If your list is bound at compile-time, you can simply use it as the attribute value in CQL, for example:

{[], se_lt_x :: [a-['ELSTON_M', 'LILLEY_N']]}

This does not require the list to be ground, merely bound. For example, this is not precluded:

foo(V1, V2):-
    {[], se_lt_x :: [a-[V1, V2]]}.

If, however, your list is not bound at compile-time, you must wrap the variable in list/1:

Bar = [a,b,c],
{[], se_lt_x :: [bar-list(Bar)]}

If you write

foo(V1):-
    {[], se_lt_x :: [a-V1]}.

and at runtime call foo([value1]), you will get a type error.

Remember: If the list of IN values is empty then no restriction is generated i.e.

{[], se_lt_x :: [a-[], b-B}

is the exactly the same as

{[], se_lt_x :: [b-B}