I tried lots of different things (pasted below) and none of them worked. I ended up using a CASE statement which worked around the issue, but I would've thought something like the command.. SELECT ( ( COLNAME > 0 )*1.000 ) AS ANY_VALUE FROM TABLENAME ; ..should give a valid response instead of an error? But I'm not sure if MonetDB wants to support this type of CAST/CONVERT operation? (None of the things I tried worked, not just the on-the-fly multiplication by 1.000). Using Feb2013-SP2 on Windows x86_64 If MonetDB should be able to convert TRUE/FALSE values to numerics, I'll submit a bug report with some PLAN and EXPLAIN results? :) Thanks for the great software!! sql>select ( mpg > 10 ) from mtcars ; +-------+ | >_mpg | +=======+ | null | | null | | true | | null | | true | | null | | true | | true | | true | | null | | null | | true | | true | | true | | true | | true | | true | | true | | true | | true | | true | | true | | true | | true | | true | | true | | true | | true | | true | | null | | true | | true | +-------+ 32 tuples (15.010ms) sql>select ( mpg > 10 )*1.000 from mtcars ; TypeException:user.s11_2[15]:'calc.sht' undefined in: _59:any := calc.sht(_57:bi t, _22:int, _23:int) TypeException:user.s11_2[17]:'bat.insert' undefined in: _62:any := bat.insert(_5 2:bat[:oid,:sht], _60:oid, _59:any) program contains errors sql>select ( ( mpg > 10 )*1.000 ) from mtcars ; TypeException:user.s12_2[15]:'calc.sht' undefined in: _59:any := calc.sht(_57:bi t, _22:int, _23:int) TypeException:user.s12_2[17]:'bat.insert' undefined in: _62:any := bat.insert(_5 2:bat[:oid,:sht], _60:oid, _59:any) program contains errors sql>select ( ( mpg >= 10 )*1.000 ) from mtcars ; TypeException:user.s13_2[15]:'calc.sht' undefined in: _59:any := calc.sht(_57:bi t, _22:int, _23:int) TypeException:user.s13_2[17]:'bat.insert' undefined in: _62:any := bat.insert(_5 2:bat[:oid,:sht], _60:oid, _59:any) program contains errors sql>select ( ( mpg >= 10 ) ) from mtcars ; +--------+ | >=_mpg | +========+ | null | | null | | true | | null | | true | | null | | true | | true | | true | | null | | null | | true | | true | | true | | true | | true | | true | | true | | true | | true | | true | | true | | true | | true | | true | | true | | true | | true | | true | | null | | true | | true | +--------+ 32 tuples (103.019ms) sql>select CAST( ( mpg >= 10 ) ) as DOUBLE from mtcars ; syntax error, unexpected ')', expecting AS in: "select cast( ( mpg >= 10 ) )" sql>select CAST( ( mpg >= 10 ) ) AS DOUBLE from mtcars ; syntax error, unexpected ')', expecting AS in: "select cast( ( mpg >= 10 ) )" sql>select CAST( mpg >= 10 ) AS DOUBLE from mtcars ; syntax error, unexpected ')', expecting AS in: "select cast( mpg >= 10 )" sql>select ( CAST( mpg >= 10 ) AS DOUBLE ) from mtcars ; syntax error, unexpected ')', expecting AS in: "select ( cast( mpg >= 10 )" sql>select ( CAST( mpg >= 10 AS DOUBLE ) from mtcars ; syntax error, unexpected FROM, expecting ')' in: "select ( cast( mpg >= 10 as do uble ) from" sql>select ( CAST( mpg >= 10 AS DOUBLE ) as x from mtcars ; syntax error, unexpected AS, expecting ')' in: "select ( cast( mpg >= 10 as doub le ) as" sql>select ( CAST( mpg >= 10 ) AS DOUBLE as x from mtcars ; syntax error, unexpected ')', expecting AS in: "select ( cast( mpg >= 10 )" sql>select CONVERT( double , mpg > 10 ) as x from mtcars; syntax error, unexpected sqlDOUBLE in: "select convert( double" sql>select CAST( TRUE as double ) from mtcars ; types boolean(1,0) and double(53,0) are not equal sql>select CAST( TRUE*1.000 as double ) from mtcars ; TypeException:user.s15_2[11]:'calc.sht' undefined in: _21:any := calc.sht(_20:bi t, _22:int, _23:int) program contains errors sql>select CAST( 'TRUE' as bit ) as z from mtcars; type (bit) unknown in: "select cast( 'TRUE' as bit )" syntax error, unexpected AS in: "as" sql>select CAST( TRUE as bit ) as z from mtcars; type (bit) unknown in: "select cast( true as bit )" syntax error, unexpected AS in: "as" sql>select CAST( TRUE as double ) as z from mtcars; types boolean(1,0) and double(53,0) are not equal sql>