Postgres mathematical expression calculated for each table row

Question

Using PostgreSQL, suppose the table looks like this:

12184 | 4 | 83 12183 | 3 | 171 12176 | 6 | 95 

How can I calculate a mathematical expression for each row of a table?

For example, to divide column 2 into column 3 so that the output is:

  12184 | 0.04819277108 12183 | 0.01754385965 12176 | 0.06315789474 

My instinct was to try:

 SELECT col1, col2 / col3 FROM table_name; 

But this returns the integer part of the ceiling (i.e. rounded), I need a floating point value.

Answer 1

A typical trick is required because col2 and col3 are integers (so the default result is an integer)

 select col1, col2/col3*1.0 from table 

or

 select col1, col2/col3::float from table 

or (standard SQL)

 select col1, col2/cast(col3 as float) from table 

Answer 2

You can use arithmetic expressions in a SELECT clause, for example:

 SELECT col1 / col2 AS new_name FROM t 

Answer 3

 select col1, col2/col3 from table; 

Must work. Are col2 and col3 numeric?

Answer 4

Try the query as follows:

 SELECT col1, col2 / col3::float FROM table_name; 

Answer 5

In PgSql, columns are printed. Therefore, if you want an operator on them; you need to specify a column.

suppose you have a column of “minutes” and you want to add “+5” to each value of the column “mintues”

Since you are adding an integer value as well, the column of minutes must be an integer, then adding can be done.

therefore, it is not true:

select *, minutes+5 from my table → Syntax error

select *, minutes::int + 5 from mytable enter output