PostgreSQL
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Chapter 9. Operators

Postgres provides a large number of built-in operators on system types. These operators are declared in the system catalog pg_operator. Every entry in pg_operator includes the name of the procedure that implements the operator and the class OIDs of the input and output types.

To view all variations of the “||” string concatenation operator, try 

    SELECT oprleft, oprright, oprresult, oprcode
    FROM pg_operator WHERE oprname = '||';

oprleft|oprright|oprresult|oprcode
-------+--------+---------+-------
     25|      25|       25|textcat
   1042|    1042|     1042|textcat
   1043|    1043|     1043|textcat
(3 rows)

Table 9-1. Postgres Operators

OperatorDescriptionUsage
< Less than?1 < 2
<= Less than or equal to?1 <= 2
<> Not equal?1 <> 2
= Equal?1 = 1
> Greater than?2 > 1
>= Greater than or equal to?2 >= 1
|| Concatenate strings'Postgre' || 'SQL'
!!= NOT IN3 !!= i
~~ LIKE'scrappy,marc,hermit' ~~ '%scrappy%'
!~~ NOT LIKE'bruce' !~~ '%al%'
~ Match (regex), case sensitive'thomas' ~ '*.thomas*.'
~* Match (regex), case insensitive'thomas' ~* '*.Thomas*.'
!~ Does not match (regex), case sensitive'thomas' !~ '*.Thomas*.'
!~* Does not match (regex), case insensitive'thomas' !~ '*.vadim*.'

Table 9-2. Postgres Numerical Operators

OperatorDescriptionUsage
! Factorial3 !
!! Factorial (left operator)!! 3
% Modulo5 % 4
% Truncate% 4.5
* Multiplication2 * 3
+ Addition2 + 3
- Subtraction2 - 3
/ Division4 / 2
: Natural Exponentiation: 3.0
; Natural Logarithm(; 5.0)
@ Absolute value@ -5.0
^ Exponentiation2.0 ^ 3.0
|/ Square root|/ 25.0
||/ Cube root||/ 27.0

Table 9-3. Postgres Geometric Operators

OperatorDescriptionUsage
+ Translation'((0,0),(1,1))'::box + '(2.0,0)'::point
- Translation'((0,0),(1,1))'::box - '(2.0,0)'::point
* Scaling/rotation'((0,0),(1,1))'::box * '(2.0,0)'::point
/ Scaling/rotation'((0,0),(2,2))'::box / '(2.0,0)'::point
# Intersection'((1,-1),(-1,1))' # '((1,1),(-1,-1))'
# Number of points in polygon# '((1,0),(0,1),(-1,0))'
## Point of closest proximity'(0,0)'::point ## '((2,0),(0,2))'::lseg
&& Overlaps?'((0,0),(1,1))'::box && '((0,0),(2,2))'::box
&< Overlaps to left?'((0,0),(1,1))'::box &< '((0,0),(2,2))'::box
&> Overlaps to right?'((0,0),(3,3))'::box &> '((0,0),(2,2))'::box
<-> Distance between'((0,0),1)'::circle <-> '((5,0),1)'::circle
<< Left of?'((0,0),1)'::circle << '((5,0),1)'::circle
<^ Is below?'((0,0),1)'::circle <^ '((0,5),1)'::circle
>> Is right of?'((5,0),1)'::circle >> '((0,0),1)'::circle
>^ Is above?'((0,5),1)'::circle >^ '((0,0),1)'::circle
?# Intersects or overlaps'((-1,0),(1,0))'::lseg ?# '((-2,-2),(2,2))'::box;
?- Is horizontal?'(1,0)'::point ?- '(0,0)'::point
?-| Is perpendicular?'((0,0),(0,1))'::lseg ?-| '((0,0),(1,0))'::lseg
@-@ Length or circumference@-@ '((0,0),(1,0))'::path
?| Is vertical?'(0,1)'::point ?| '(0,0)'::point
?|| Is parallel?'((-1,0),(1,0))'::lseg ?|| '((-1,2),(1,2))'::lseg
@ Contained or on'(1,1)'::point @ '((0,0),2)'::circle
@@ Center of@@ '((0,0),10)'::circle
~= Same as'((0,0),(1,1))'::polygon ~= '((1,1),(0,0))'::polygon

The time interval data type tinterval is a legacy from the original date/time types and is not as well supported as the more modern types. There are several operators for this type.

Table 9-4. Postgres Time Interval Operators

OperatorDescriptionUsage
#< Interval less than?
#<= Interval less than or equal to?
#<> Interval not equal?
#= Interval equal?
#> Interval greater than?
#>= Interval greater than or equal to?
<#> Convert to time interval
<< Interval less than?
| Start of interval
~= Same as
<?> Time inside interval?

Users may invoke operators using the operator name, as in: 

select * from emp where salary < 40000;
Alternatively, users may call the functions that implement the operators directly. In this case, the query above would be expressed as: 
select * from emp where int4lt(salary, 40000);

psql has a \dd command to show these operators.

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