how this "and" function in sql works?

Question

This is my query

select *
from employement 
where emp_addr = 'varanasi' and emp_addr = 'delhi'

if all the conditions separated by and are true then it will display records but here both the conditions are true still am not getting anything?

Answer 1

Your WHERE clause is specifying that a column in a given record simultaneously has two different values:

where emp_addr = 'varanasi' and emp_addr = 'delhi'

This is impossible, so you always get back no result set. Perhaps you intended to OR together these criteria:

where emp_addr = 'varanasi' or emp_addr = 'delhi'

Or, perhaps you want to find all groups of records which have both these addresses present:

SELECT some_col
FROM yourTable
WHERE emp_addr IN ('varanasi', 'delhi')
GROUP BY some_col
HAVING MIN(emp_addr) <> MAX(emp_addr);

Answer 2

使用IN

select * from employement where emp_addr in ('varanasi','delhi')

Answer 3

How can emp_addr='varanasi' and emp_addr='delhi'? No records will ever match.