PHP Learning practiced Hand (Fri)

Basic exercises for MySQL database

2. Create a database
   
   
4. Working with databases
   
   
6. Create a table
   
   • Char: fixed-length constant
   • VARCHAR: variable
     
     
8. Show Table
   
   
10. View table Structure
    
    
12. Inserting data
    SHA1 (): Encrypt data function, create an encrypted word a, which is exactly 40 characters long
    
    
14. View all elements
    
    

16. WHERE Condition Statement
    

18. Between ...
    
    

20. Like/not like

    • Wildcard _: matches a single character;%: matches 0 or more characters
    • Precede the wildcard with (\), then _ or% is only the original symbol and does not have a wildcard meaning.
    • Queries with like conditional statements are generally slow because the index cannot be used, so this format should be used only when absolutely necessary

22. Sort order BY ascending ASC Descending desc

    • To sort the columns that are enum types, sorting is based on the order in which the enum values are created by the column.
      

24. Limit

    • LIMIT x: Returns the first X record in the query record
    • LIMIT x, y: Returns the Y record starting with the X record
    • The limit clause does not improve the execution speed of the query because MySQL still has to assemble each record together, and then truncate the list
      

26. Update, delete
    
    • To prevent yourself from accidentally updating too many rows, you can apply a limit clause to update
    • Clears a table, preferring truncate:truncate table tablename
    • To delete all the data in the table and the table itself: Drop table tablename;
    • To delete an entire database: Drop DB databasename
      
      
28. Concat connection function
    
    
30. CONCAT_WS Connection function
    
    
32. Length function
    
    
34. Format function
    
    
36. Concat in combination with the Format function
    
    
38. Rand () function
    
    
40. Now (), Curtime (), curdate () function
    
    
42. Date_format function
    

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