Best way to ignore null values in MYSQL - mysql

Question

My data looks like this,
I have multiple values in the Table field with each having its own unique values for the Data field. However, Data values for TableA will be the same format in the table myTable. Same applies to all records in the Table field.
I am using JSON_EXTRACT to get the value in conjunction with CASE statements.
SELECT
CASE
WHEN
Table = 'table A'
THEN
CONCAT_WS('\n','Name: ',
JSON_EXTRACT(Data, '$.name'))
END AS 'tableA',
CASE
WHEN
Table = 'table B'
THEN
CONCAT_WS('\n','Location: ',
JSON_EXTRACT(Data, '$.fieldType'))
END AS 'tableB' from myTable
The problem with this is that I will be getting null values.
I am getting the below results,
I am expecting the below results,
I want to avoid the null values. Is there any other way to extract the data ? I am using MYSQL.

Answer 1

Option one:
Select *
from ( SELECT CASE WHEN Table_c = 'table A' THEN
CONCAT_WS('\n','Name: ', JSON_EXTRACT(data_c, '$.name'))
END AS 'TableA'
from test_t) A,
( SELECT CASE WHEN Table_c = 'table B' THEN
CONCAT_WS('\n','Location: ', JSON_EXTRACT(data_c, '$.fieldType'))
END AS 'TableB'
from test_t) B
where TableA is not null
and TableB is not null
Option two:
SELECT CASE WHEN Table_c = 'table B' THEN
CONCAT_WS('\n','Location: ', JSON_EXTRACT(data_c, '$.fieldType'))
ELSE
CONCAT_WS('\n','Name: ', JSON_EXTRACT(data_c, '$.name'))
END AS 'Data'
, CASE WHEN Table_c = 'table B' THEN
'Table B'
ELSE
'Table A'
END AS 'Table'
from test_t
Here is the demo
Please note that I have changed the names of the table and columns in my demo.

Answer 2

I think you just want conditional aggregation:
SELECT MAX(CASE WHEN Table = 'table A'
THEN CONCAT_WS('\n', 'Name: ', JSON_EXTRACT(Data, '$.name'))
END) AS tableA,
MAX(CASE WHEN Table = 'table B'
THEN CONCAT_WS('\n','Location: ', JSON_EXTRACT(Data, '$.fieldType'))
END) AS tableB
from myTable;
If there could be multiple matches in the JSON, then you might want GROUP_CONCAT() instead:
SELECT GROUP_CONCAT(CASE WHEN Table = 'table A'
THEN CONCAT_WS('\n', 'Name: ', JSON_EXTRACT(Data, '$.name'))
END) AS tableA,
GROUP_CONCAT(CASE WHEN Table = 'table B'
THEN CONCAT_WS('\n','Location: ', JSON_EXTRACT(Data, '$.fieldType'))
END) AS tableB
from myTable;

Answer 3

Note: you have to understand these are not actual null values in database but because your requirement is to read and convert the rows to columns and thus each row in the final result will have null value for all columns other than the corresponding derived one. We can use max on each column (each "CASE" as in your query).
You could try with below,
SELECT MAX(IF(data_type = 'TableA', CONCAT_WS('\n', 'Name: ',
JSON_EXTRACT(data, '$.name'))
, ''))
TableA,
MAX(IF(data_type = 'TableB', CONCAT_WS('\n', 'Location: ',
JSON_EXTRACT(data, '$.fieldType')), ''))
TableB
FROM mytable