SQL 中 ALTER 和 UPDATE 命令的区别
原文:https://www . geesforgeks . org/alter-and-update-command-in-SQL/之间的差异
1。更改命令:
ALTER SQL 命令是一个 DDL(数据定义语言)语句。ALTER 用于更新数据库中表的结构(如添加、删除、修改数据库中表的属性)。
语法:
// add a column to the existing table
ALTER TABLE tableName
ADD columnName columnDefinition;
// drop a column from the existing table
ALTER TABLE tableName
DROP COLUMN columnName;
// rename a column in the existing table
ALTER TABLE tableName
RENAME COLUMN olderName TO newName;
// modify the datatype of an already existing column in the table
ALTER TABLE table_name
ALTER COLUMN column_name column_type;
2。更新命令:
更新命令是一个数据操作语言语句。它用于操作任何现有列的数据。但是不能被改变表的定义。
语法:
// table name that has to update
UPDATE tableName
// which columns have to update
SET column1 = value1, column2 = value2, ...,columnN=valueN.
// which row you have to update
WHERE condition
注意:如果没有 WHERE 子句，表中的所有记录都将被更新。
SQL 中 ALTER 和 UPDATE 命令的区别:
| -你好。不，不 | ALTER command | 更新命令 | | --- | --- | --- | | one | The ALTER command is data definition language (DDL). | Update command is a data manipulation language. | | Two | The Alter command will perform actions at the structure level instead of the data level. | The update command will be executed at the data level. | | three | Command is used to add, delete and modify the attributes of relationships (tables) in the database. | The UPDATE command is used to update the existing records in the database. | | four | Command initializes the values of all tuples to NULL by default. | The update command sets the value specified in the command to the tuple. | | five | This command changes the table structure. | This command modifies the data in the table. | | six | Example: table structure, table name, SP, function, etc. | Example: Change data rows or columns in a table, etc. |版权属于：月萌API www.moonapi.com，转载请注明出处
