Which are the boolean symbols

I want to select TRUE from a table which include a boolean field.
When displayed the field show 3 icons

  1. an empty square
  2. a checked square
  3. a dash in the square

how to select any of these “values” by a SQL “WHERE” condition ?


The three icons are a tristate setting - TRUE, FALSE or undefined. The WHERE conditions:

    this is checked square

    this is empty square

    this is dash in square

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Empty square indicates FALSE

Tick in square indicates TRUE

Black square inside square indicates NULL

For the WHERE clause use =FALSE, =TRUE, IS NULL