Introduction and advanced level of MySQL (12)

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Exist as a condition at the location of the query condition

adopt = lead ⼊ Of ⼦ Inquire about , Must return a single value . Only match ⼀⾏. The value is ⼀ individual , But it can be combined
If only ⼀⾏⼀ The return value of the column is only ⼀ individual , Then you can. = > < >= <= in not in also ⾏
Eg: Find the same as Tan Ming ⼀ Urban Science ⽣ Information
Eg2： Find all the students with the lowest score ⽣ Information
– Subquery ： The query result exists as the comparison value of the search condition
– Inquire about the student information in the same city as Ma Yu
select city from studentinfo where studentname=‘ Ma Yu ’
select * from studentinfo where city=‘ Shangqiu ’
– = matching , You must ensure that the value returned by the sub query is only one row and one column
select * from studentinfo where city=(select city from studentinfo where
studentname=‘ Ma Yu ’)
– > < != in( There can be multiple line ranges ) not IN
– Query the student information with the lowest score
select min(exam) from exam
select * from exam where exam=45
select * from studentinfo where studentid=‘2011001011’
select * from studentinfo where studentid=(
select studentid from exam where exam=(
select min(exam) from exam ) )
IN 、ANY 、ALL Of ⽐ Comparison operator quotation ⼊ On the list of ⼦ Inquire about （ Multiple columns can be returned ）
If the return value is multiple ⾏ Under the circumstances ： Can't make ⽤=> < these , Sure ⽤in not in >anyall <all These keywords

--  Query the student information with the lowest score : If there is only one person with the lowest score , Then you can. =
 --  If there are many people , Must use in
 select min(exam) from exam
 select * from exam where exam=45
 select * from studentinfo where studentid in('2011001011','2011001003')
 select * from studentinfo where studentid in(
 select studentid from exam where exam=(
 select min(exam) from exam
 )
 )