MySQL concat() creates column names to be used in queries?

To create column names to be used in queries, you need to use user-defined variables via the set command. The syntax is as follows -

SET @anyVariableName := ( SELECT CONCAT ( "SELECT", GROUP_CONCAT(CONCAT(" 1 as ", COLUMN_NAME) SEPARATOR ','), " FROM DUAL") FROM INFORMATION_SCHEMA_COLUMNS WHERE TABLE_NAME= ‘yourTableName’ );

Now use the PREPARE command to prepare the statement. The syntax is as follows -

PREPARE anyVariableName from @anyVariableName;

Use the EXECUTE command to execute the statement. The syntax is as follows -

EXECUTE anyVariableName;

Use the DEALLOCATE command to deallocate the prepared statement. The syntax is as follows -

DEALLOCATE PREPARE anyVariableName;

We will now create a table with two columns and this column will be used in the join query. The query to create the table is as follows -

mysql> create table ConcatenationWithUserDefinedVariable -> ( -> Id int NOT NULL AUTO_INCREMENT, -> User_Id int, -> PRIMARY KEY(Id) -> ); Query OK, 0 rows affected (1.14 sec)

Use the above syntax for the column names to be used in the query. The query is as follows -

mysql> set @q := ( -> select concat( -> "select", -> group_concat(concat(" 1 as ", column_name) separator ','), -> "from dual") -> from information_schema.columns -> where table_name = 'ConcatenationWithUserDefinedVariable'); Query OK, 0 rows affected (0.01 sec)

The query to prepare the above user-defined variables is as follows -

mysql> prepare stmt from @q; Query OK, 0 rows affected (0.00 sec) Statement prepared

Now execute the statement prepared above. The query is as follows -

mysql> execute stmt;

The following is the output -

+----+---------+ | Id | User_Id | +----+---------+ | 1 | 1 | +----+---------+ 1 row in set (0.00 sec)

Finally, you need to release the prepared statement. The query is as follows -

mysql> deallocate prepare stmt; Query OK, 0 rows affected (0.00 sec)

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