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/*
 * 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 com.hazelcast.org.apache.calcite.rex;

import javax.annotation.Nonnull;

/** Policy for whether a simplified expression may instead return another
 * value.
 *
 * 

In particular, it deals with converting three-valued logic (TRUE, FALSE, * UNKNOWN) to two-valued logic (TRUE, FALSE) for callers that treat the UNKNOWN * value the same as TRUE or FALSE. * *

Sometimes the three-valued version of the expression is simpler (has a * smaller expression tree) than the two-valued version. In these cases, * favor simplicity over reduction to two-valued logic. * * @see RexSimplify */ public enum RexUnknownAs { /** Policy that indicates that the expression is being used in a context * Where an UNKNOWN value is treated in the same way as FALSE. Therefore, when * simplifying the expression, it is acceptable for the simplified expression * to evaluate to FALSE in some situations where the original expression would * evaluate to UNKNOWN. * *

SQL predicates ({@code WHERE}, {@code ON}, {@code HAVING} and * {@code FILTER (WHERE)} clauses, a {@code WHEN} clause of a {@code CASE} * expression, and in {@code CHECK} constraints) all treat UNKNOWN as FALSE. * *

If the simplified expression never returns UNKNOWN, the simplifier * should make this clear to the caller, if possible, by marking its type as * {@code BOOLEAN NOT NULL}. */ FALSE, /** Policy that indicates that the expression is being used in a context * Where an UNKNOWN value is treated in the same way as TRUE. Therefore, when * simplifying the expression, it is acceptable for the simplified expression * to evaluate to TRUE in some situations where the original expression would * evaluate to UNKNOWN. * *

This does not occur commonly in SQL. However, it occurs internally * during simplification. For example, "{@code WHERE NOT expression}" * evaluates "{@code NOT expression}" in a context that treats UNKNOWN as * FALSE; it is useful to consider that "{@code expression}" is evaluated in a * context that treats UNKNOWN as TRUE. * *

If the simplified expression never returns UNKNOWN, the simplifier * should make this clear to the caller, if possible, by marking its type as * {@code BOOLEAN NOT NULL}. */ TRUE, /** Policy that indicates that the expression is being used in a context * Where an UNKNOWN value is treated as is. This occurs: * *

    *
  • In any expression whose type is not {@code BOOLEAN} *
  • In {@code BOOLEAN} expressions that are {@code NOT NULL} *
  • In {@code BOOLEAN} expressions where {@code UNKNOWN} should be * returned as is, for example in a {@code SELECT} clause, or within an * expression such as an operand to {@code AND}, {@code OR} or * {@code NOT} *
* *

If you are unsure, use UNKNOWN. It is the safest option. */ UNKNOWN; /** Returns {@link #FALSE} if {@code unknownAsFalse} is true, * {@link #UNKNOWN} otherwise. */ public static @Nonnull RexUnknownAs falseIf(boolean unknownAsFalse) { return unknownAsFalse ? FALSE : UNKNOWN; } public boolean toBoolean() { switch (this) { case FALSE: return false; case TRUE: return true; default: throw new IllegalArgumentException("unknown"); } } public RexUnknownAs negate() { switch (this) { case TRUE: return FALSE; case FALSE: return TRUE; default: return UNKNOWN; } } }





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