Why I figure can run normally, and figure 2 more subfields count (*) are not, I can't statistics sub-fields first? In figure 1, figure 2) three figure (figure 4) for the database content

CodePudding user response:

Error in the use of the

The select academy, count (*) as number of readers from the reader where the exists (select library card number, the count (*) as number of borrow books from library registration where readers borrow books number=. Library card number group by library card number having the count (*) & gt;=2) group by college of the order by the count (*) desc

CodePudding user response:

What is the difference between this and the in!

CodePudding user response:

The count (*) to the count (library card number) give it a try

CodePudding user response:

By introducing the IN (or NOT) IN the query result is one zero or more values, the subquery return results after external query will use these results,

Sub-fields much count (*) get a few columns?

CodePudding user response:

The count (*) to the count not (library card number)

CodePudding user response:

The

reference, on the third floor of the 4th floor response:

through (or NOT) IN the introduction of the child IN the query result is one zero or more values, the subquery return results after external query will use these results,

Sub-fields much count (*) get a few columns?

What this mean,, I just learned it's not too understand