/// <summary> /// For CASE statements which represent boolean values: /// /// CASE XXX /// WHEN AAA THEN true ===> (XXX==AAA) || (XXX==BBB) /// WHEN BBB THEN true /// ELSE false /// etc. /// END /// /// Also, /// /// CASE XXX /// WHEN AAA THEN false ===> (XXX!=AAA) && (XXX!=BBB) /// WHEN BBB THEN false /// ELSE true /// etc. /// END /// /// The reduce to a conjunction or disjunction of equality or inequality. /// The possibility of NULL in XXX is taken into account. /// </summary> private SqlExpression TryToWriteAsSimpleBooleanExpression(Type caseType, SqlExpression discriminator, List <SqlWhen> newWhens, bool allValuesLiteral) { SqlExpression rewrite = null; if (caseType == typeof(bool) && allValuesLiteral) { bool?holdsNull = SqlExpressionNullability.CanBeNull(discriminator); // The discriminator can't hold a NULL. // In this case, we don't need the special fallback that CASE-ELSE gives. // We can just construct a boolean operation. bool?whenValue = null; for (int i = 0; i < newWhens.Count; ++i) { SqlValue lit = (SqlValue)newWhens[i].Value; // Must be SqlValue because of allValuesLiteral. bool value = (bool)lit.Value; // Must be bool because of caseType==typeof(bool). if (newWhens[i].Match != null) // Skip the ELSE { if (value) { rewrite = sql.OrAccumulate(rewrite, sql.Binary(SqlNodeType.EQ, discriminator, newWhens[i].Match)); } else { rewrite = sql.AndAccumulate(rewrite, sql.Binary(SqlNodeType.NE, discriminator, newWhens[i].Match)); } } else { whenValue = value; } } // If it could possibly hold null values. if (holdsNull != false && whenValue != null) { if (whenValue == true) { rewrite = sql.OrAccumulate(rewrite, sql.Unary(SqlNodeType.IsNull, discriminator, discriminator.SourceExpression)); } else { rewrite = sql.AndAccumulate(rewrite, sql.Unary(SqlNodeType.IsNotNull, discriminator, discriminator.SourceExpression)); } } } return(rewrite); }