Knowledge about SQL - DML

DML: Add, delete and modify the data in the table

1. Add data ：

        * grammar ：

                insert into Table name （ Name 1, Name 2,..... Name n）value( value 1, value 2,..... value n);

        * Be careful ：

                1. Column name and value should correspond one by one .

                2. If the name comes after , No column name defined , The default is to add values to all columns .

                         insert into Table name value( value 1, value 2,..... value n);

                3. Except for the number type , Use quotation marks for other types （ Single and double can ） Lead up

2. Delete data ：

        * grammar ：

                delete from Table name [where Conditions ]

        * Be careful ：

               1. If there is no condition , All records in the table will be deleted .

               2. If you want to delete all records

                      1.delete from Table name ;-- It is not recommended to use . The number of records is the number of delete operations

                      2.truncate table Table name ; -- Recommended . Efficient , Delete the table first , Generating an identical table .

3. Modifying data ：

        * grammar ：

                update Table name set Name 1 = value 1, Name 2 = value 2,...[where Conditions ];

        * Be careful ：

                1. If no condition is added , All records in the table will be newly modified .