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;
Related
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.
I need to call a mySQL function for all columns in a table.
I know how to do it for a particular column
Like this:
UPDATE `table_name` set `column_name` = function_name(`column_name`)
But i have no clue how to do it for all columns at once.
Thanks in advance.
Little clarification: I dont want to manually mention all columns, as i probably could have 200 columns table.
But i have no clue how to do it for all columns at once.
You just can't - there is no such shortcut in the update syntax.
You can do this with a single update statement, but you need to enumerate each and every column, like:
update table_name set
column_name1 = function_name(column_name1),
column_name2 = function_name(column_name2),
column_name3 = function_name(column_name3)
An alternative would be to use dynamic SQL to programatically generate the proper query string from catalog table information_schema.columns, and then execute it. This seems uterly complicated for what looks like a one-shot task... But here is sample code for that:
-- input variables
set #table_schema = 'myschema';
set #table_name = 'mytable';
set #function_name = 'myfunction';
-- in case "GROUP_CONCAT()" returns more than 1024 characters
set session group_concat_max_len = 100000;
-- build the "set" clause of the query string
select
#sql := group_concat(
'`', column_name, '` = ', #table_schema, '.', #function_name, '(`', column_name, '`)'
separator ', '
)
from information_schema.columns
where table_schema = #table_schema and table_name = #table_name;
-- entire query string
set #sql := concat('update ', #table_schema, '.', #table_name, ' set ', #sql);
-- debug
select #sql mysql;
-- execute for real
prepare stmt from #sql;
execute stmt;
deallocate prepare stmt;
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;
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
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: