Simple Expressions

Logical Expressions

Logical Operators lists the operators and calculation rules of logical expressions.

Comparative Expressions

Comparison Operators lists the common comparative operators.

In addition to comparative operators, you can also use the following sentence structure:

• BETWEEN

  The operator BETWEEN...AND selects a data range between two values. These values can be numeric, text, or date.

  The expression a BETWEEN x AND y is equivalent to the expression a >= x AND a <= y.

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  SELECT 2 BETWEEN 1 AND 3 AS RESULT; result ---------- t (1 row) SELECT 2 >= 1 AND 2 <= 3 AS RESULT; result ---------- t (1 row)

  a NOT BETWEEN x AND y is equivalent to a < x OR a > y.

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  SELECT 2 NOT BETWEEN 1 AND 3 AS RESULT; result ---------- f (1 row) SELECT 2 < 1 OR 2 > 3 AS RESULT; result ---------- f (1 row)

• To check whether a value is null, use:

  1 2	expression IS NULL expression IS NOT NULL

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  SELECT 2+2 IS NULL AS RESULT; result ---------- f (1 row) SELECT 2+2 IS NOT NULL AS RESULT; result ---------- t (1 row)

  or an equivalent (non-standard) sentence structure:

  1 2	expression ISNULL expression NOTNULL

  

  Do not write expression=NULL or expression<>(!=)NULL, because NULL represents an unknown value, and these expressions cannot determine whether two unknown values are equal.

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  SELECT 2+2 ISNULL AS RESULT; result ---------- f (1 row) SELECT 2+2 NOTNULL AS RESULT; result ---------- t (1 row)

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  SELECT 2+2 IS DISTINCT FROM NULL AS RESULT; result ---------- t (1 row) SELECT 2+2 IS NOT DISTINCT FROM NULL AS RESULT; result ---------- f (1 row)