How to concatenate strings in a Select statement in MySQL - mysql

Question

I have to run a query in SQL Server using data from a MySQL database. When I needed to do the opposite, I found an easy way to accomplish what I needed writing an update query using the select statement in SQL Server.
In SQL Server I wrote:
SELECT 'update sgidb.Example set MySQLCol1 = ' + cast(MSSQLCol1 as varchar(max)) + ' where MySQLCol2 = ' + cast(MSSQLCol2 as varchar(max)) + ';' FROM MSSQLTable
That resulted in a bunch of update statements with the keys I needed like:
'update sgidb.Example set MySQLCol1 = 12 where MySQLCol2 = 45;
But when I tried to do the same in MySQL I got a bunch of syntax errors. The web told me MySQL don't need the + operator to concatenate strings in a sentence, but it didn't work, neither writing the concatenate function explicitly. Any ideas?

Answer 1

You can use the CONCAT function which is available in MySQL as well as in SQL, like this:
SELECT CONCAT('update sgidb.Example set MySQLCol1 = ' , MSSQLCol1 , ' where MySQLCol2 = ' , MSSQLCol2 , ';' )FROM MSSQLTable
Now in the above solution you need to take care of the blank space after or before or even after and before the statement.
For tackling the above situation what you can do is to use the function CONCAT_WS, which is available in MySQL as well as in SQL:
SELECT CONCAT_WS(' ', 'update sgidb.Example set MySQLCol1 =' , MSSQLCol1 , 'where MySQLCol2 =' , MSSQLCol2 , ';' )FROM MSSQLTable
CONCAT_WS function adds two or more strings together with a separator.
Now no need to take care of the spaces that you need to put to avoid the syntax error anymore.
Please note that, CONCAT_WS is going to handle null as well. But in case of CONCAT, if any of the variable/field is null then the entire CONCATENATED result becomes null.

Answer 2

Here's how you can do it
SELECT concat("update sgidb.Example set MySQLCol1 = ",MSSQLCol1,"where MySQLCol2 = ",MSSQLCol2,";") FROM MSSQLTable;

Answer 3

Both SQL Server and mysql have got CONCAT function.
You can use the below query in both RDBMS.
SELECT CONCAT('update sgidb.Example set MySQLCol1 = ' , MSSQLCol1 , ' where MySQLCol2 = ' , MSSQLCol2 , ';' )FROM MSSQLTable

Answer 4

You may try concat to concatenate your string.
Example as:
SELECT CONCAT('MySQL CAST example #',CAST(2 AS CHAR));
#ouput
MySQL CAST example #2
In your above update query your set and where column may have varchar, but if you closely look into your query ' is missing in both of the column names. Please try the below query.
SELECT CONCAT('update sgidb.Example set MySQLCol1 = ''',
CAST(MSSQLCol1 AS VARCHAR(MAX)),
''' where MySQLCol2 = ''',
CAST(MSSQLCol2 AS VARCHAR(MAX)) ,
''';' )
FROM MSSQLTable;