SQL Learning Summary (5)--sql Database modification Technology

5.1 Data Insertion

Insert into table name (field name, field name,...) Values (field value, field value,...)

5.2 Data Update

Update tablename Set columnname1=value1 [, columnname2=value2 ...] [Where Condition]

Note: One can only change the data in one table; The new value of the column can be either a specified constant or an expression, or it can be data from another table, and if not, all records for the entire table are modified.

5.3 Data Deletion

Delete from TableName [Where condition]

Note: You can only delete data from one table at a time; Delete Deletes only the records in the table, does not delete the table; Delete cannot delete the values of individual columns, but instead deletes the entire record, and removes all records from the entire table if no conditions are added.

Delete data records from the entire table:

Delete from worker backup truncate table worker backup

Note: Delete actually performs a delete operation on each record in the table, and the database executes all tasks that are likely to occur, such as all tasks such as triggers; the TRUNCATE statement deletes all records at once, ignoring the trigger, faster than delete. However, truncate does not handle other events caused by the deletion, which can create a database integrity problem, and it is best to use Delete for tables that have dependencies.

SQL Learning Summary (5)--sql Database modification Technology