WHERE Clause

The WHERE clause specifies the conditions the results of the query should comply with. See below the syntax for specifying conditions.

Syntax for a list of conditions
<condition> ::=
    <condition> AND <condition>
  | <condition> OR <condition>
  | NOT <condition>
  | ( <condition> )
  | <value> <binary operator> <value> [ , <value> ]*
  | <value> <binary operator> ( <value> [ , <value> ]* )
  | <value> BETWEEN <value> AND <value>
  | <value> <unary operator>

A condition is a sequence of condition elements separated by the logical operators AND, OR or NOT. At evaluation time, it obtains a boolean result. The conditions can be grouped between the symbols ( and ) to vary their priority.

A condition is comprised of three elements: a left-side operator which will be the one to which the condition is applied, an operator and zero, one or several right-side operands, depending on the operator used. The comparison operators supported by Virtual DataPort are specified in section Comparison Operators; they include operators of equality, greater/lesser comparison, string contention, etc.

A condition operand can be the name of an attribute, a constant, an expression to be evaluated or a compound value (see the section below).

Conditions with Compound Values

The ROW constructor creates register values (see section Management of Compound Values for more details about compound types). For example:

ROW (value1, ... ,valueN)

creates a register value with N fields. Each value can be an attribute, a literal, a number, a logical value, an expression to evaluate or a new ROW element.

To create array values use the ROW construct combined with { and }. For example:

{ ROW (value1, ... ,valueN), ROW (valueN+1, ... ,value2N) }

This creates an array value containing two register values. All the registers of an array have to have the same type.

Note

See Rules for forming functions for a formal description of the syntax to create compound values.

Conditions with compound values can only be used with the equality (=) and inequality (<>) operators. Both operands must have compatible types for the comparison to be possible.