Collection of common operations of msyql (function, joint query, etc.) + sql instance

1. Display the column information of the table, an example is as follows:

   #The table name is t_category_base
   show full COLUMNS from t_category_base

2.  The conversion of string and time, the example is as follows:

   #Character creation time, accurate to year, month, day, hour, minute and second
   STR_TO_DATE('2016-01-02','%Y-%m-%d %T')
   
   #Time to string, accurate to year, month, day, hour, minute, second, take the createdate attribute (timestamp type) of the query table test as an example
   select DATE_FORMAT(createdate,'%Y-%m-%d %T') as createdate from test where createdate is not null;                                                                            

3. %Y: represents a 4-digit year
   %y: represents the year of 2
    
   %m: represents month, the format is (01...12)  
   %c: represents month, the format is (1...12)
    
   %d: represents the number of days in the month, the format is (00...31)  
   %e: represents the number of days in the month, the format is (0...31)
    
   %H: represents the hour, the format is (00...23)  
   %k: represents the hour, the format is (0...23)  
   %h: represents the hour, the format is (01...12)  
   %I: represents the hour, the format is (01...12)  
   %l : represents the hour, the format is (1...12)
     
   %i: Represents minutes, the format is (00...59)
    
   %r: represents time, the format is 12 hours (hh:mm:ss [AP]M)  
   %T: represents time, the format is 24 hours (hh:mm:ss)       

4. After the union query is grouped by id, use GROUP_CONCAT to combine multiple attributes separated by commas to form a new attribute. The example is as follows:

   #One is the student table student with fields id, student_name, school_id, the other is the school table school with two fields id, school_name
   # insert data separately
   insert into student values(1,'tom',1);
   insert into student values(2,'jim',1);
   insert into school values(1,'qinghua school');
   
   #Joint query, use group_concat to combine student names, group by school id
   select sl.school_name,group_concat(st.name) as student_name from student st,school sl where st.school_Id = sl.id group by sl.id                                                

   
5. mysql convert string to case

   # Convert to lowercase
   LCASE('string');
   
   # to uppercase
   UCASE('string')