How to combine different columns of a table to yield a single column in query output in PostgreSQL?

Suppose you have a table user_info that contains the state and district of different users. An example is given below −

Now, if you want to combine the state and district in a single field called location, this is how you should be able to do it −

SELECT name, district || ', ' || state as location from user_info

The || operator is the string concatenation operator. The output will be −

Similar operations can also be performed on numerical values. Suppose you have a table marks containing the total marks scored by students and the maximum possible marks. An example is given below −

Now, if you wish to output a new column containing percentage marks, based on marks_scored and max_marks, you can do that as follows −

SELECT name, marks_scored*100.0/max_marks as perc from marks

The output will look like this −