Value expressions are the general expression language used to produce values for conditions, SELECT expressions, filters, and clauses like WHERE, ORDER BY, and GROUP BY. The expression syntax of DDSQL is a superset of SQL expression syntax.

Arithmetic operators

DDSQL supports standard binary and unary infix arithmetic notation from SQL and many other languages:

The standard order of operations applies. To control the order of operations, add parentheses: (5 - 2) * 3.

Comparison operators

DDSQL implements the following comparison operators:

For tag references and tag groups, the equality operator (=) is treated as a “contains” comparison. See the Querying Tags in DDSQL for more details.

Additionally, DDSQL supports the following SQL keywords, which function as standard boolean operators:

• NOT
• AND
• OR

DDSQL also supports the following comparator keywords as they are defined in the SQL standard:

• IS NULL
• IS NOT NULL
• LIKE
• NOT LIKE
• IN
• NOT IN

DDSQL supports the BETWEEN keyword such that a BETWEEN x AND y is equivalent to a >= x AND a <= y. See the Postgres documentation for BETWEEN for details.

Logical operators

CASE

The CASE expression is a generic conditional expression, similar to if/else statements in other programming languages. CASE comes in two forms, simple and searched.

Simple CASE statements

Simple CASE statements use the following syntax:

CASE expression
  WHEN value THEN result
  [ WHEN ... ]
  [ ELSE result ]
END

The expression is computed, then compared to each of the value expressions in the WHEN clauses until one is found that is equal to it. If no match is found, the result of the ELSE clause, or NULL if ELSE is omitted, is returned.

Searched CASE statements

Searched CASE statements use the following syntax:

CASE
  WHEN condition THEN result
  [ WHEN ... ]
  [ ELSE result ]
END

If a condition’s result is true, the value of the CASE expression is the result that follows the condition, and the remainder of the CASE expression is not processed. If the condition’s result is not true, any subsequent WHEN clauses are examined in the same manner. If no WHEN condition yields true, the value of the CASE expression is the result of the ELSE clause. If the ELSE clause is omitted and no condition is true, the result is NULL.

CAST

CAST specifies a conversion from one data type to another.

Syntax

CAST(expression AS type)

Not all types are convertible in this way.

DDSQL also supports Postgres casting syntax:

expression::type

For example, SELECT 1::text;.