First published on WeChat: SQL Database Operations and Maintenance
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The differences between alter, update, and modify are: different modifications, different declarations, and different executions.
I. Modifications are different
1. alter: alter modifies the data structure of the table (modify is a usage of alter).
2、update：update modifies the data content of the table.
3, modify: modify modify the field type and length, that is, modify the attributes of the field, modify the field type and length.
II. Differences in statements
1. alter: alter is used when declaring a modified database.
2、update: update is used when declaring a modified table.
3, modify: modify in the declaration of the modified file to use.
III. Different implementation
1. alter: alter takes effect when the execution of the command is completed.
2、update：update to execute the "commit" statement after the command will take effect.
3、modify：modify execution of the command to complete that will take effect.