Limit the columns displayed in a MYSQL pivot table - mysql

The Question:
How do I limit the number of columns displayed/produced on a MYSQL pivot table?
My Setup:
I have a table named "updates" that looks like the following:
I have the following snippet of query (This is only part of the query, the whole thing only adds more columns from other tables but this is the only section that gets pivoted):
SET #sql = NULL;
SELECT
GROUP_CONCAT(DISTINCT
CONCAT(
'MAX(IF(Date = ''',
Date,
''', Description, NULL)) AS ',
CONCAT("'",Date_Format(Date, '%d/%m/%Y'),"'")
)
)INTO #sql
FROM updates;
SET #sql = CONCAT('SELECT Action, ', #sql, ' FROM updates GROUP BY Action');
PREPARE stmt FROM #sql;
EXECUTE stmt;
The result of this query is as follows:
As you can see, this pivots the table as intended with the dates as columns. However, there is potential for these updates (to actions) to become very long before they are "closed" and not displayed. Therefore, I would like to limit the outcome to the latest 3 updates. BUT..Not per action as this would potentially still give me a lot of updates in the pivot table.
I would like to have the most recent 3 dates from the updates table with all updates for each date keeping this pivot format.
Example: The outcome table above would look the same but with the exception of the columns titled "02/10/2016" and "04/10/2016".
Thanks in advance for any assistance or advise.

For anyone else trying to solve this issue, I managed to use the following query to produce the desired results:
SET #sql = NULL;
SELECT
GROUP_CONCAT(DISTINCT
CONCAT(
'MAX(IF(Date = ''',
Date,
''', Description, NULL)) AS ',
CONCAT("'",Date_Format(Date, '%d/%m/%Y'),"'")
) ORDER BY Date ASC
) INTO #sql
FROM (
SELECT * FROM updates
GROUP BY Date
ORDER BY Date DESC
LIMIT 2)
AS updates;
SET #sql = CONCAT('SELECT Action, ', #sql, ' FROM updates GROUP BY Action');
PREPARE stmt FROM #sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

Related

Create an insert to pivot value pair values into a table

I have a value pair table that I want to use to create a member table
Based on Taryns answer to this question
MySQL pivot table query with dynamic columns
I have this code that creates selects the data, which works fine
SELECT
GROUP_CONCAT(DISTINCT
CONCAT(
'MAX(CASE WHEN wpdg_usermeta.meta_key = ''',
meta_key,
''' THEN wpdg_usermeta.meta_value END) `',
meta_key, '`'
)
) INTO #sql
FROM
wpdg_usermeta
WHERE
wpdg_usermeta.meta_key like "member_%"
;
SET #sql = CONCAT('SELECT user_id, ', #sql, '
FROM wpdg_usermeta
GROUP BY user_id');
PREPARE stmt FROM #sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
So, my question is - does anyone know how I could alter this to run an INSERT instead of a SELECT so that I could populate the new member table?
You want to create a new table with the results of the dynamic query. I think the simplest approach is to use the create table ... as select ... syntax.
This requires very few changes to your code, and allow you to create the table on the fly based on the results of the query:
SET #sql = CONCAT(
'CREATE TABLE member AS SELECT user_id, ',
#sql,
' FROM wpdg_usermeta GROUP BY user_id'
);
Note that the datatypes of the new table are inferred from the query's metadata; this might, or might no, to exactly what you want. You can check the documentation for more detaiils.

Debugging MySQL pivot row into dynamic number of columns

I recently came across the thread below, and it was very useful in building a dynamic SQL for MySQL.
MySQL pivot row into dynamic number of columns
With that said, I did struggle with trying to debug the statement. Now for the real purpose of this post! To debug, I would run a Select on my variable containing the statement (Select #SQL). Then copy that result from the viewer windows and have the query analyzer review it. Once I did this, development really sped up. I am sure this is known by all the advance pro developers but for any newbies, I hope this help!
My dynamic statement looks like this as a reference.
SET #sql = NULL;
SET ##group_concat_max_len = 50000;
SELECT
GROUP_CONCAT(DISTINCT
CONCAT(
' sum(
case when symbol = ''',
symbol,
''' then pctttlassets end) AS ',
CONCAT(UPPER(ACode),'_',REPLACE(Symbol, '+', ''))
)
) INTO #sql
from trade_detail this;
SET #sql = CONCAT('SELECT Distinct(main.port_code) as PortCode, ', #sql, '
FROM trade_detail main GROUP BY main.Port_Code');
SELECT #SQL;
PREPARE stmt FROM #sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

Rewriting multiple SQL commands into a single query

I am trying to turn this statement:
SET #sql = NULL;
SELECT
GROUP_CONCAT(DISTINCT
CONCAT(
'max(case when year = ',
year,
' then experience_rate end) AS `',
year, '-Pen`'
) ORDER BY year
) INTO #sql
FROM
spooner_pec;
SET #sql = CONCAT('SELECT policy_number, primary_name, ', #sql, '
FROM spooner_pec
GROUP BY policy_number');
PREPARE stmt FROM #sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
Into something like this:
SELECT policy_number, primary_name, (SELECT GROUP_CONCAT(DISTINCT CONCAT('max(case when year = ', year, ' then experience_rate end) AS `', year, '-Pen`') ORDER BY year))
FROM spooner_pec
GROUP BY policy_number
But as you can see by the fiddle, I am getting some strange output as a column instead of the actual columns, what am I doing wrong here?
SQLFiddle
I generally do regular expression search to get all the code in single line or selected code in single line.
Use find & replace
1. Under find section type "\n" --find all next line keywords
2. Under replace section type " " -- replace \n with one blank space
3. Tick "Use Regular Expression"
Your result will be in single line.
Before
After
Replace with section is a blank space
*Note: This approach works on Windows platform and most of the editors.

Execute statement only returns #Rows

I'm using PMA to test some pivot queries (dynamic columns), everything seems to be working just fine however, I'm only getting the # Rows in my results, not the actual set of rows.
How can I see my result set?
SET #sql = NULL;
SELECT
GROUP_CONCAT(DISTINCT
CONCAT(
'MAX(IF(t.week_end = ''',
t1.week_end,
''', t.st_hours, NULL)) AS ''',
t1.week_end, '\''
)
) INTO #sql
FROM timesheets t1 WHERE t1.week_end > "2015-03-01";
SET #sql = CONCAT('SELECT t.assignment_id
, ', #sql, '
FROM timesheets t
LEFT JOIN timesheets t1 ON t.timesheet_id = t1.timesheet_id
GROUP BY t.assignment_id');
PREPARE stmt FROM #sql;
EXECUTE stmt;
Returns # Rows: 440
SELECT * FROM table - Returns the actual set of rows
This will be resolved in the latest PHPMyAdmin builds, and should be released in version 4.6.
[Prepared statements] can be sent in query as this pretty much works in phpMyAdmin right now. The only problem is displaying results. If you execute all of above, you get result just from last query (DEALLOCATE), which shows 0 rows, but if you do it without DEALLOCATE, you reportedly get 1 row, but it's not displayed.
Reference

Determine max number of character in a field

The field size of the MySQL daabase I'm working on have been determine quite arbitrary and I'd like to review them based on its current data. So I'd like to determine the maximum number of character per field so I'm sure I won't lose any data when I update the field size.
Is there a feature in phpmyadmin or a SQL statement that can help me?
Thanks
use CHAR_LENGTH, ex
SELECT MAX(CHAR_LENGTH(column1)) maxCol1,
MAX(CHAR_LENGTH(column2)) maxCol2,
MAX(CHAR_LENGTH(column3)) maxCol3
FROM tableName
SQLFiddle Demo
You can also use Dynamic SQL if you have unknown number of columns. All you need to supply is the name of the database and the name of the table,
SET #db_Name = 'db_2_21a29';
SET #tb_name = 'TABLENAME';
SET #sql = NULL;
SELECT
GROUP_CONCAT(DISTINCT
CONCAT('MAX(CHAR_LENGTH(', COLUMN_NAME, ')) AS `', COLUMN_NAME, '`')
) INTO #sql
FROM information_schema.columns
WHERE TABLE_NAME = #tb_name AND
TABLE_SCHEMA = #db_Name;
SET #sql = CONCAT('SELECT ',#sql, 'FROM ', #tb_name);
PREPARE stmt FROM #sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
SQLFiddle Demo
In phpmyadmin you are able to know this data from the Structure tab of your table. look at the attached image: