I want to calculate how many NULL there are in each column of the table. But I don t want to write as: SELECT SUM(CASE WHEN columns1 IS NULL THEN 0 ELSE 1), SUM(CASE WHEN columns2 IS NULL THEN 0 ELSE 1), SUM(CASE WHEN columns3 IS NULL TH...
SELECT T.[ID] AS ID, A.UserName AS , T. AS , T. AS , W.[ID] AS ID, B.UserName AS , W. AS , W. AS , X.[ID] AS ID, C.UserName AS , X. AS , X. AS FROM ( SELECT MX.[ID], SUM (CONVER...
now there is a tree structure: id pid name 10 qq 21 ww 3 1 ee the result I need is 10 qq 2 21 ww 0 31 ee 0 query all nodes and the number of children of the corresponding nodes. How should I write sql? ...
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period = 573 SHYA= sqldf( select PPMONTH, REGION, WEARSEG, sum(uncal_value) as uncal_value from Ftable where region in ("Shanghai") and WEARSEG in ("Men","Women") and PPMONTH in (period) group...
how does 1.mysql export a data table of 6 million records? 2. I ve tried that direct export will overload the database. ...
how does mysql export a data table from the beginning to the end of a field? ...
in wordpress, the attachment is saved in the same table as the article, but all the information in the attachment is saved according to the following format. Why this format? by the way, how did this format come from? a:5:{s:5:"width";i:800...
recently, I am working on a book information management system. There is a table marc that stores the information of books. There are more than 20 fields in it. when importing data, it is required to check the duplicates according to 7 fields, and the...
I am doing a blog, article list page entries, need to show the article title, plus the user name. currently there is only the user s id in the article table. excuse me, how is it better to relate to user information in this case ...
how to check the total number of records returned by answering query conditions in query pagination: select top 10 * from (select row_number() over(order by id asc) as rownumber,* from com_system_menu) temp_row where rownumber>((2-1)*10); the nu...
I want to implement the function of , which returns all questions under all tags that the user follows and sorts them in chronological order. Tag and Question are many-to-many, User and Question are one-to-many, and user and tag are many-to-many I ...
A table field has 3 records returned by separate query B table field alone query has 8 records returned currently these two tables have no primary key and foreign key if you want to combine, how should the structure of the table be designed an...
how is Zhihu s database designed? what I don t understand is how Zhihu s questions and concerns are designed? agree with the answer, focus on the question, and how is it stored? ...
Why can mysql save time with varchar and still make time comparisons? What is the principle? Y-m-d H:i:s like this ...
problem description I used SQLAlchemy to build a SQLite database to store literature data. Now I want to check the number of authors of each article. The author and the document are stored in two separate tables, using the identification number of the...
I use native php5.6 to write blog want to click on the column, appear under this column of the article, but how to appear all the articles. sources of topics and their own ideas mysqli took out all the columns but couldn t use them. related code...
suppose there is a compound index index_abcd, and the query statement where a = " " and b = " " and c > " " and d = " " at this time c > " " is invalid. How to optimize ?...
seniors, I want to splice the existing fields and fill them in the new fields, such as original table < table > < thead > < tr > < th > id < th > < th > name < th > < th > date < th > < th > record_id < th > < tr > < thead > < tbody > < tr...
is the rollback of the transaction a failure of sql execution or a success of sql execution, but will be rolled back if the number of rows affected by additions, deletions and changes is 0? ...