Learn and practice PHP (5)

Basic exercises for MySQL database

1. Creating a database
   
   

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2. Using a database
   
   

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3. Creating a table
   
   • char: Fixed length, constant
   • varchar: Variable
     
     

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4. Display table
   
   

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5. View table structure
   
   

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6. Insert data
   SHA1(): Encrypt data function, create an encrypted character creation, its length is exactly 40 characters
   
   

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7. View all elements
   
   

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8. WHERE conditional statement
   

   

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9. between … and…
   
   

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10. LIKE / NOT LIKE

    • Wildcard _: matches a single character; %: matches If 0 or more characters
    • are added with () before the wildcard character, then _ or % are only used as original symbols and have no wildcard meaning.
    • Queries with LIKE conditional statements are generally slower because they cannot take advantage of indexes, so this format should only be used when absolutely necessary

    

    

    

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11. Sort order by ascending ASC Descending DESC

    • The column to be sorted is of type ENUM, and the sorting will be based on the order in which the ENUM values ​​were created in the column.
      

    

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12. limit

    • LIMIT Will improve query execution speed, because mysql still has to gather each record together and then truncate the list
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13. update, delete
    
    • To prevent yourself from accidentally updating too many rows, you can apply a limit clause to update
    • To clear a table, the preferred truncate: TRUNCATE TABLE tablename
    • To delete all data in the table and Table itself: DROP TABLE tablename;
    • To delete the entire database: DROP DATABASE databasename
      
      

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14. concat connection function
    
    

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15. concat_ws connection function
    
    

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16. length function
    
    

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17. format function
    
    

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18. concat is used with format function
    
    

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19. rand() function
    
    

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20. now(), curtime(), curdate( ) function
    
    

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21. date_format function
    

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