Boolean Type
Boolean Type
Tacnode provides the standard SQL type boolean
; seeTable 7.18. The boolean
type can have several states: “true”, “false”, and a third state, “unknown”, which is represented by the SQL null value.
Table Boolean Data Type
Name | Storage Size | Description |
---|---|---|
boolean | 1 byte | state of true or false |
Boolean constants can be represented in SQL queries by the SQL key words TRUE
, FALSE
, and NULL
.
The datatype input function for type boolean
accepts these string representations for the “true” state:
true |
yes |
on |
1 |
and these representations for the “false” state:
false |
no |
off |
0 |
Unique prefixes of these strings are also accepted, for example t
or n
. Leading or trailing whitespace is ignored, and case does not matter.
The datatype output function for type boolean
always emits either t
or f
, as shown in Example 7.2.
Example Using the boolean
Type
The key words TRUE
and FALSE
are the preferred (SQL-compliant) method for writing Boolean constants in SQL queries. But you can also use the string representations by following the generic string-literal constant syntax described inSection 3.1.2.7, for example 'yes'::boolean
.
Note that the parser automatically understands that TRUE
and FALSE
are of type boolean
, but this is not so for NULL
because that can have any type. So in some contexts you might have to cast NULL
to boolean
explicitly, for example NULL::boolean
. Conversely, the cast can be omitted from a string-literal Boolean value in contexts where the parser can deduce that the literal must be of type boolean
.