![]() ![]() If one expression is a DT_DBTIMESTAMP2 data type, the other expression is implicitly converted to DT_DBTIMESTAMP2 and a DT_DBTIMESTAMP2 comparison is performed. For more information, see Integration Services Data Types in Expressions. If one expression is a DT_DBTIMESTAMPOFFSET data type, the other expression is implicitly converted to DT_DBTIMESTAMPOFFSET and a DT_DBTIMESTAMPOFFSET comparison is performed. When the two expressions evaluate to the same data type, a comparison of that data type is performed. ![]() When comparing the expressions, the system applies the following conversion rules in the order listed: Notice that IS UNKNOWN and IS NOT UNKNOWN are effectively the same as IS NULL and IS NOT NULL, respectively, except that the input expression must be of Boolean type.The system does not support comparisons between an expression that evaluates to a time data type and an expression that evaluates to either a date or a date/time data type. A null input is treated as the logical value "unknown". These will always return true or false, never a null value, even when the operand is null. Thus, these constructs effectively act as though null were a normal data value, rather than "unknown".īoolean values can also be tested using the constructs expression IS TRUE Similarly, IS NOT DISTINCT FROM is identical to = for non-null inputs, but it returns true when both inputs are null, and false when only one input is null. However, if both inputs are null it returns false, and if only one input is null it returns true. When this behavior is not suitable, use the IS DISTINCT FROM constructs: expression IS DISTINCT FROM expression expression IS NOT DISTINCT FROM expressionįor non-null inputs, IS DISTINCT FROM is the same as the operator. For example, 7 = NULL yields null, as does 7 NULL. Ordinary comparison operators yield null (signifying "unknown"), not true or false, when either input is null. This definition conforms to the SQL standard, and is a change from the inconsistent behavior exhibited by PostgreSQL versions prior to 8.2. Because of this behavior, IS NULL and IS NOT NULL do not always return inverse results for row-valued expressions, i.e., a row-valued expression that contains both NULL and non-null values will return false for both tests. Note: If the expression is row-valued, then IS NULL is true when the row expression itself is null or when all the row's fields are null, while IS NOT NULL is true when the row expression itself is non-null and all the row's fields are non-null. (The null value represents an unknown value, and it is not known whether two unknown values are equal.) This behavior conforms to the SQL standard. Or the equivalent, but nonstandard, constructs: expression ISNULLĭo not write expression = NULL because NULL is not "equal to" NULL. To check whether a value is or is not null, use the constructs: expression IS NULL If it is not, those two arguments are automatically swapped, so that a nonempty range is always implied. All comparison operators are binary operators that return values of type boolean expressions like 1 = x AND a yīETWEEN SYMMETRIC is the same as BETWEEN except there is no requirement that the argument to the left of AND be less than or equal to the argument on the right. It is not possible to implement != and operators that do different things.Ĭomparison operators are available for all relevant data types. Note: The != operator is converted to in the parser stage.
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