Mysql Practice Summary

I. Summary

First Review: Connection query (several tables linked together to form a large table in the query---easy to forget) sub-query joint query see the basic article

Build the table order: first build the main table and then build the content from the table to fill in the main table before filling out from the table

Parentheses:

1. Parentheses can represent the part of the independent operation

2. With parentheses is the method  () For example , count (); where to find the specified line:

#--- check the records of all students in class 95033 and class 95031.  Selectfrom  where student.sno=score.sno and Course.cnoclass= ' 95033 ' class='95031')

Key Words :

commas are important; almost all statements can be nested using

Select:   From , where , Group by have; Order by

distanct;   or; in;  and; Not

1.not:not in (see Front Mysqle Foundation) and not-like

#- Query student table in the "King" of the classmate record. Select * from Student where Sname don't like' King%'

2. When the group by and where, COUNT (*) is used with the note [notation with parentheses}

Define first: a function that performs a calculation on a column in a set of rows and returns a single value. 1.whereand having a simple, where condition is a field, and a having condition can be a field or a aggregation function; it is important that where is the filter source data, having much to do with group by, and the condition is often the aggregation function; when there is a group By, it has to be behind the group by condition, and where is in front of group by. Aggregation function: Sum,count,avg ... And so on;2. Count and Sumcount are ' cumulative '; sum is ' accumulate ', or the table A_info above, and the number of people with scores greater than 60 in each grade and their average score:3the execution order of the. SQL statement: (1） fromSelect a data source;2）wherefilter the data source;3Group by groups the filtered data sources;4) is calculated using the aggregate function;5) Having the data to filter the groupings;6) evaluates an expression;7) Order by sort;

Group where COUNT (*) is also used to explain

#---- Check the class number of at least 2 men.  Selectclass from Student  where ssex=' man ' class having count (*) >=2

3.DISTANCT: See the basic part of the method of use not to repeat

4. get time and date see the next blog below for a brief

Gets an integer that can be compared for size:

Gets the year (Time column name)----column name is not quoted

Gets the current time date (now ())

Get Day date (the column where the time is)

#---- Query the name and age of each student in the student table. the Select from student#--- queries the maximum and minimum sbirthday date values in the Student table.  Select from studentunionSelect from student#---  Query all records in the student table in order of class number and age from large to small.  Selectfromclass

Mysql Practice Summary