Mysql display field name where value is specific - mysql

Question

I have a table like this:
+------------------------+-------+------+-------+------+
| user | TELPE | CRS2 | MECAN | GOPI |
+------------------------+-------+------+-------+------+
| user1.foo#my-email.com | NULL | NULL | 1 | NULL |
+------------------------+-------+------+-------+------+
| user2.foo#my-email.com | 1 | NULL | 1 | NULL |
+------------------------+-------+------+-------+------+
I'm struggling to find the request that would returned the columns name for a specific user where the value is 1.
Select manually column is not an option as if there is only 4 columns today,
there'll may be 300 next week.
for instance the search for the user1 would give this this result:
+-------------+
| Books |
+-------------+
| MECAN |
+-------------+
and for user2:
+-------------+
| Books |
+-------------+
| TELPE |
+-------------+
| MECAN |
+-------------+
My Mysql skills are not very high so any help is appreciated,
Many thanks by advance.

Answer 1

You need to convert the columns into rows this process is called unpivot.
You can do that with UNIONS.
Query
SELECT
USER
, TELPE AS 'column_value'
, 'TELPE' AS 'column_source'
FROM
users
WHERE
TELPE = 1
UNION ALL
SELECT
USER
, CRS2 AS 'column_value'
, 'CRS2' AS 'column_source'
FROM
users
WHERE
CRS2 = 1
UNION ALL
SELECT
USER
, MECAN AS 'column_value'
, 'MECAN' AS 'column_source'
FROM
users
WHERE
MECAN = 1
UNION ALL
SELECT
USER
, GOPI AS 'column_value'
, 'GOPI' AS 'column_source'
FROM
users
WHERE
GOPI = 1
Result
user column_value column_source
---------------------- ------------ ---------------
user2.foo#my-email.com 1 TELPE
user1.foo#my-email.com 1 MECAN
user2.foo#my-email.com 1 MECAN
Now we can use this query as a delivered table to filter the results you need.
Query
SELECT
DISTINCT
column_source
FROM (
SELECT
USER
, TELPE AS 'column_value'
, 'TELPE' AS 'column_source'
FROM
users
WHERE
TELPE = 1
UNION ALL
SELECT
USER
, CRS2 AS 'column_value'
, 'CRS2' AS 'column_source'
FROM
users
WHERE
CRS2 = 1
UNION ALL
SELECT
USER
, MECAN AS 'column_value'
, 'MECAN' AS 'column_source'
FROM
users
WHERE
MECAN = 1
UNION ALL
SELECT
USER
, GOPI AS 'column_value'
, 'GOPI' AS 'column_source'
FROM
users
WHERE
GOPI = 1
)
AS
users
WHERE
users.user = 'user1.foo#my-email.com'
AND
users.column_value = 1
Result
| column_source |
|---------------|
| MECAN |
demo http://www.sqlfiddle.com/#!9/3ed091/19
EDITED
Select manually column is not an option as if there is only 4 columns today, there'll may be 300 next week.
Then you need to move to dynamic SQL generating.
First when are going to need a number generator this query will generate 1000 numbers from 2 to 1001.
Why we need a number generator will become more clear later on.
Query
SELECT
#row := #row + 1 AS number
FROM (
SELECT 0 UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9
)
AS row1
CROSS JOIN (
SELECT 0 UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9
)
AS row2
CROSS JOIN (
SELECT 0 UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9
)
AS row3
CROSS JOIN (
SELECT #row := 1
)
AS init_user_param
Result
number
2
3
4
5
6
7
8
9
10
....
....
990
991
992
993
994
995
996
997
998
999
1000
1001
Now we need a way to get all the column fore the table users.
Query
SELECT
GROUP_CONCAT(COLUMN_NAME) AS COLUMN_NAME
FROM
information_schema.COLUMNS
WHERE
TABLE_NAME = 'users'
AND
TABLE_SCHEMA <> 'performance_schema'
Result
COLUMN_NAME
----------------------------
user,TELPE,CRS2,MECAN,GOPI
Now we want to generate a unique list like
user TELPE
user CRS2
...
...
user GOPI
Now we combine the number generator with the query to get the columns.
We also use SUBSTRING_INDEX to spilt the comma separated values.
Query
SELECT
DISTINCT
SUBSTRING_INDEX(SUBSTRING_INDEX(COLUMN_NAME, ',', 1), ',', -1) column1
, SUBSTRING_INDEX(SUBSTRING_INDEX(COLUMN_NAME, ',', generator.number), ',', -1) column2
FROM (
SELECT
GROUP_CONCAT(COLUMN_NAME) AS COLUMN_NAME
FROM
information_schema.COLUMNS
WHERE
TABLE_NAME = 'users'
AND
TABLE_SCHEMA <> 'performance_schema'
)
AS user_column
CROSS JOIN (
SELECT
#row := #row + 1 AS number
FROM (
SELECT 0 UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9
)
AS row1
CROSS JOIN (
SELECT 0 UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9
)
AS row2
CROSS JOIN (
SELECT 0 UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9
)
AS row3
CROSS JOIN (
SELECT #row := 1
)
AS init_user_param
)
AS generator
Result
column1 column2
------- ---------
user TELPE
user CRS2
user MECAN
user GOPI
To make to SQL generation completely dynamic
Query
SET #sql_union = NULL;
SELECT
GROUP_CONCAT(
CONCAT(
"
SELECT
",column1,"
, ",column2," AS 'column_value'
, '",column2,"' AS 'column_source'
FROM
users
WHERE
",column2," = 1
"
)
SEPARATOR 'UNION ALL'
)
FROM (
SELECT
DISTINCT
SUBSTRING_INDEX(SUBSTRING_INDEX(COLUMN_NAME, ',', 1), ',', -1) column1
, SUBSTRING_INDEX(SUBSTRING_INDEX(COLUMN_NAME, ',', generator.number), ',', -1) column2
FROM (
SELECT
GROUP_CONCAT(COLUMN_NAME) AS COLUMN_NAME
FROM
information_schema.COLUMNS
WHERE
TABLE_NAME = 'users'
AND
TABLE_SCHEMA <> 'performance_schema'
)
AS user_columns
CROSS JOIN (
SELECT
#row := #row + 1 AS number
FROM (
SELECT 0 UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9
)
AS row1
CROSS JOIN (
SELECT 0 UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9
)
AS row2
CROSS JOIN (
SELECT 0 UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9
)
AS row3
CROSS JOIN (
SELECT #row := 1
)
AS init_user_param
)
AS generator
)
AS generator_union_sql INTO #sql_union;
SET #sql = CONCAT(
"
SELECT
DISTINCT
column_source
FROM (
"
,#sql_union,
"
)
AS
users
WHERE
users.user = 'user1.foo#my-email.com'
AND
users.column_value = 1
"
);
PREPARE queryUser FROM #sql;
EXECUTE queryUser;
Result
column_source
---------------
MECAN

Answer 2

I suspect you are looking for something like
SELECT user, if(telpe=1,"TELPE","") as rTELPE, if(CRS2=1,"CRS2","") as rCRS2 from myTable

Answer 3

What I understand for your question is:
SELECT 'TELPE' FROM yourTable WHERE telpe = 1 AND user = 'user1.foo#my-email.com'
UNION ALL
SELECT 'CRS2 ' FROM yourTable WHERE crs2 = 1 AND user = 'user1.foo#my-email.com'
UNION ALL
SELECT 'MECAN' FROM yourTable WHERE mecam = 1 AND user = 'user1.foo#my-email.com'
UNION ALL
SELECT 'GOPI' FROM yourTable WHERE gopi = 1 AND user = 'user1.foo#my-email.com'