/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to you under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.eigenbase.sql;
/**
* SqlNullSemantics defines the possible comparison rules for values which might
* be null. In SQL (and internal plans used to process SQL) different rules are
* used depending on the context.
*/
public enum SqlNullSemantics {
/**
* Predicate semantics: e.g. in the expression (WHERE X=5), if X is NULL,
* the comparison result is unknown, and so a filter used to evaluate the
* WHERE clause rejects the row.
*/
NULL_MATCHES_NOTHING,
/**
* GROUP BY key semantics: e.g. in the expression (GROUP BY A,B), the key
* (null,5) is treated as equal to another key (null,5).
*/
NULL_MATCHES_NULL,
/**
* Wildcard semantics: logically, this is not present in any SQL construct.
* However, it is required internally, for example to rewrite NOT IN to NOT
* EXISTS; when we negate a predicate, we invert the null semantics, so
* NULL_MATCHES_NOTHING must become NULL_MATCHES_ANYTHING.
*/
NULL_MATCHES_ANYTHING
}
// End SqlNullSemantics.java