Prepend text to MySQL columns' names - mysql

Question

Supposing a query such as:
SELECT * FROM tableA;
How can I prepend a_ to each columns' name? For example if there is a column "username" it would be accessed in the results as "a_username".
EDIT: The SELECT username AS a_username format will not help as I need to continue using the * field selection. There is a JOIN and a potential conflict with a returned column from another table in the JOIN. I will be iterating over the returned columns (foreach) and only want to output the columns that came from a particular table (whose schema may change) to HTML input fields where a site admin could edit the fields' content directly. The SQL query in question looks like SELECT firstTable.*, anotherTable.someField, anotherTable.someOtherField and their exists the possibility that someField or someOtherField exists in firstTable.
Thanks.

Answer 1

You can use the INFORMATION_SCHEMA.COLUMNS table to formulate the query and then use dynamic SQL to execute it.
First let's make a sample database called dotancohen and a table called mytable
mysql> drop database if exists dotancohen;
Query OK, 1 row affected (0.03 sec)
mysql> create database dotancohen;
Query OK, 1 row affected (0.00 sec)
mysql> use dotancohen
Database changed
mysql> create table mytable
-> (
-> id int not null auto_increment,
-> username varchar(30),
-> realname varchar(30),
-> primary key (id)
-> );
Query OK, 0 rows affected (0.06 sec)
mysql> insert into mytable (realname,username) values
-> ('rolando','odnalor'),('pamela','alemap'),
-> ('dominique','euqinimod'),('diamond','dnomaid');
Query OK, 4 rows affected (0.05 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> select * from mytable;
+----+-----------+-----------+
| id | username | realname |
+----+-----------+-----------+
| 1 | odnalor | rolando |
| 2 | alemap | pamela |
| 3 | euqinimod | dominique |
| 4 | dnomaid | diamond |
+----+-----------+-----------+
4 rows in set (0.00 sec)
mysql>
Here is the metadata table called INFORMATION_SCHEMA.COLUMNS:
mysql> desc INFORMATION_SCHEMA.COLUMNS;
+--------------------------+---------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------------------------+---------------------+------+-----+---------+-------+
| TABLE_CATALOG | varchar(512) | NO | | | |
| TABLE_SCHEMA | varchar(64) | NO | | | |
| TABLE_NAME | varchar(64) | NO | | | |
| COLUMN_NAME | varchar(64) | NO | | | |
| ORDINAL_POSITION | bigint(21) unsigned | NO | | 0 | |
| COLUMN_DEFAULT | longtext | YES | | NULL | |
| IS_NULLABLE | varchar(3) | NO | | | |
| DATA_TYPE | varchar(64) | NO | | | |
| CHARACTER_MAXIMUM_LENGTH | bigint(21) unsigned | YES | | NULL | |
| CHARACTER_OCTET_LENGTH | bigint(21) unsigned | YES | | NULL | |
| NUMERIC_PRECISION | bigint(21) unsigned | YES | | NULL | |
| NUMERIC_SCALE | bigint(21) unsigned | YES | | NULL | |
| CHARACTER_SET_NAME | varchar(32) | YES | | NULL | |
| COLLATION_NAME | varchar(32) | YES | | NULL | |
| COLUMN_TYPE | longtext | NO | | NULL | |
| COLUMN_KEY | varchar(3) | NO | | | |
| EXTRA | varchar(27) | NO | | | |
| PRIVILEGES | varchar(80) | NO | | | |
| COLUMN_COMMENT | varchar(1024) | NO | | | |
+--------------------------+---------------------+------+-----+---------+-------+
19 rows in set (0.02 sec)
mysql>
What you need from this table are the following columns:
table_schema
table_name
column_name
ordinal_position
What you are asking for is to have the column_name and the column_name prepended with a_
Here is the query and how to execute it:
select concat('select ',column_list,' from ',dbtb) into #newsql
from (select group_concat(concat(column_name,' a_',column_name)) column_list,
concat(table_schema,'.',table_name) dbtb from information_schema.columns
where table_schema = 'dotancohen' and table_name = 'mytable'
order by ordinal_position) A;
select #newsql;
prepare stmt from #newsql;
execute stmt;
deallocate prepare stmt;
Let's execute it
mysql> select concat('select ',column_list,' from ',dbtb) into #newsql
-> from (select group_concat(concat(column_name,' a_',column_name)) column_list,
-> concat(table_schema,'.',table_name) dbtb from information_schema.columns
-> where table_schema = 'dotancohen' and table_name = 'mytable'
-> order by ordinal_position) A;
Query OK, 1 row affected (0.01 sec)
mysql> select #newsql;
+--------------------------------------------------------------------------------+
| #newsql |
+--------------------------------------------------------------------------------+
| select id a_id,username a_username,realname a_realname from dotancohen.mytable |
+--------------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> prepare stmt from #newsql;
Query OK, 0 rows affected (0.00 sec)
Statement prepared
mysql> execute stmt;
+------+------------+------------+
| a_id | a_username | a_realname |
+------+------------+------------+
| 1 | odnalor | rolando |
| 2 | alemap | pamela |
| 3 | euqinimod | dominique |
| 4 | dnomaid | diamond |
+------+------------+------------+
4 rows in set (0.01 sec)
mysql> deallocate prepare stmt;
Query OK, 0 rows affected (0.00 sec)
mysql>
Give it a Try !!!
You mentioned in your question : The SELECT username AS a_username format will not help as I need to continue using the * field selection.
All you have to do to implement my suggestion is run the query using tableA as follows:
select concat('select ',column_list,' from ',dbtb) into #newsql
from (select group_concat(concat(column_name,' a_',column_name)) column_list,
concat(table_schema,'.',table_name) dbtb from information_schema.columns
where table_schema = DATABASE() and table_name = 'tableA'
order by ordinal_position) A;
When you retrieve that query result, just use it as the query to submit to mysql_query.

Answer 2

You'll need to list the columns, e.g
SELECT username AS a_username FROM tableA;
alternatively, post-process in back-end, e.g. change the array keys in your code

Answer 3

Create a view with renamed columns, e.g. -
CREATE VIEW a_view AS SELECT username AS a_username FROM table;
Then refer to this view.

Answer 4

As already mentioned, there is no standard way to mass-prefix column names in a regular query.
But if you really wanted to achieve it, you could write a stored procedure which would query information_schema to get a list of columns in a table, and then prefix them one by one. After that it's possible to concatenate a query as string, PREPARE and EXECUTE it.
A downside to this approach is the fact that you cannot join on a stored procedure's result. But of course, you could as well create a stored procedure for each type of query you issue. Prefixing the fields for any table could then be made a separate generic FUNCTION.
All of this stuff sounds to me like an overkill, though. I would recommend either renaming the actual columns, so that they are always prefixed, or just listing all the result fields with AS aliases, as Scibuff and Alister suggested.

Answer 5

I don't believe it can be done for all columns automatically, but you can list as many columns as you like with AS
SELECT id AS a_id,
name AS a_name,
email AS a_email /*, etc....*/
FROM tableA;
I've only inserted newlines for some extra clarity.