Mysql JOIN子查询

Question

How should I do query where

• I have (table1) row which can have none or several rows referencing to it in other table
• These referencing (table2) rows have colum1 that can be null or date

I would like to have all rows from table1 which have all rows column1 not as null or no rows at all, in table2.

Of course the basic sql goes like:

SELECT table1.* FROM table1 JOIN table2 ON table2.id = table1.table2_id

But what comes next?

Answer 1

You can count the occurences of null in your query like SUM(CASE WHEN table2.col IS NULL THEN 1 ELSE 0 END) AS nullcount , i assume table2.col is the one which has date of null in it

SELECT 
  table1.*,
  SUM(
    CASE
      WHEN table2.col IS NULL 
      THEN 1 
      ELSE 0 
    END
  ) AS nullcount 
FROM
  table1 
  JOIN table2 
    ON table2.id = table1.table2_id 
HAVING nullcount > 0