How to use SQL alias with variable

Question

I have the following code:

set @a='city_name';
select place_names from table1 tbl1 inner join table2 tbl2 
   on tbl1.city_name = tbl2.city_name

Here I need to use variable @a with alias tbl1 . Something like tbl1.@a and tbl2.@a .

How can I do this?

Thanks in advance.

Answer 1

Syntax, including column names and other identifiers, must be fixed at the time the statement is parsed.

The only way to use a user variable as part of SQL syntax is to use a prepared statement, so you can build a SQL statement as a string before it is parsed.

SET @a='city_name';

SET @sql=CONCAT('select place_names from table1 tbl1 inner join table2 tbl2 
   on tbl1.', @a, ' = tbl2.', @a);

PREPARE stmt1 FROM @sql;
EXECUTE stmt;