ALTER Command in SQL vs. UPDATE Command in SQL: Know the Difference
By Shumaila Saeed || Published on August 8, 2024
The ALTER command in SQL modifies the structure of a database table, while the UPDATE command changes the data within a table.
Key Differences
The ALTER command in SQL is used to change the structure of database tables. It can add, delete, or modify columns and their data types. The UPDATE command, conversely, is used to modify the data within the table rows without altering the table's structure.
Shumaila Saeed
Aug 08, 2024
With the ALTER command, you can change a table's schema, like adding a new column or changing a column's data type. The UPDATE command, however, is used for updating existing records in a table with new data values.
Shumaila Saeed
Aug 08, 2024
The ALTER command is typically used less frequently, as structural changes to tables are not common in day-to-day operations. In contrast, the UPDATE command is commonly used in routine database operations to modify existing data.
Shumaila Saeed
Aug 08, 2024
One key aspect of the ALTER command is its ability to set or change constraints, such as primary keys or foreign keys. The UPDATE command, however, is focused solely on changing field values in the database rows.
Shumaila Saeed
Aug 08, 2024
Using the ALTER command can have significant implications on database integrity and requires careful planning. The UPDATE command, while powerful, primarily deals with the manipulation of the data within the existing framework of the table.
Shumaila Saeed
Aug 08, 2024
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Comparison Chart
Operations
Add/delete/modify columns or constraints
Change values of existing records
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Aug 08, 2024
Frequency of Use
Less frequent, structural changes
Common for routine data modifications
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Aug 08, 2024
Typical Application
Schema redesign, adding constraints
Data maintenance, corrections
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Aug 08, 2024
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ALTER Command in SQL and UPDATE Command in SQL Definitions
ALTER Command in SQL
Change Data Type
ALTER TABLE Orders ALTER COLUMN OrderDate DATETIME;
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UPDATE Command in SQL
Change Multiple Records
UPDATE Books SET Price = Price * 1.1 WHERE Year = 2020;
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ALTER Command in SQL
Delete Column
ALTER TABLE Products DROP COLUMN Description;
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UPDATE Command in SQL
Conditional Data Update
UPDATE Orders SET Status = 'Shipped' WHERE OrderDate < '2023-01-01';
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ALTER Command in SQL
Modify Table Structure
ALTER TABLE Customers ADD Email VARCHAR(255);
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UPDATE Command in SQL
Modify Existing Data
UPDATE Students SET Grade = 'A' WHERE StudentID = 123;
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UPDATE Command in SQL
Increment Numeric Values
UPDATE Accounts SET Balance = Balance - 100 WHERE AccountID = 456;
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ALTER Command in SQL
Set Constraints
ALTER TABLE Users ADD CONSTRAINT PK_Users PRIMARY KEY (UserID);
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UPDATE Command in SQL
String Manipulation
UPDATE Employees SET Email = CONCAT(FirstName, '.', LastName, '@company.com');
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Repeatedly Asked Queries
Can UPDATE command change the structure of a table?
No, it only changes the data within the table.
Shumaila Saeed
Aug 08, 2024
Is it possible to change the data type of a column using ALTER command?
Yes, ALTER command can change column data types.
Shumaila Saeed
Aug 08, 2024
What does the UPDATE command do in SQL?
It modifies the data within table rows.
Shumaila Saeed
Aug 08, 2024
How does the UPDATE command identify which rows to update?
It uses a WHERE clause to specify the rows.
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Aug 08, 2024
Can ALTER command be used to delete columns?
Yes, it can delete columns from a table.
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Aug 08, 2024
What is the main use of ALTER command in SQL?
It's used to modify the structure of a database table.
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Aug 08, 2024
Can ALTER command add a new column to a table?
Yes, it can add new columns to a table.
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Aug 08, 2024
Is UPDATE command used for adding new records?
No, UPDATE is for modifying existing records, not adding new ones.
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Aug 08, 2024
Can ALTER command set primary keys?
Yes, it can set or change primary keys.
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Aug 08, 2024
How is UPDATE command used for numeric calculations?
It can perform calculations on numeric fields, like incrementing values.
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Aug 08, 2024
What precautions are needed when using ALTER command?
It requires careful planning as it affects the database structure.
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Aug 08, 2024
Is it possible to undo an UPDATE command?
Without a backup or transaction, undoing an UPDATE can be difficult.
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Aug 08, 2024
Can UPDATE command be used on multiple rows at once?
Yes, it can update multiple rows based on the WHERE clause.
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Aug 08, 2024
Does ALTER command affect existing data?
It can, especially when changing data types or deleting columns.
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Aug 08, 2024
Can ALTER command modify constraints?
Yes, it can add, modify, or remove constraints.
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Aug 08, 2024
Is the UPDATE command complex to use?
It's straightforward but requires careful specification of conditions.
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Aug 08, 2024
How does UPDATE handle string data?
It can modify string data, including concatenation and replacement.
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Aug 08, 2024
How frequently is ALTER command used compared to UPDATE?
ALTER is used less frequently, as table structures don’t change often.
Shumaila Saeed
Aug 08, 2024
Can UPDATE command affect the performance of a database?
Yes, especially when updating large numbers of rows.
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Aug 08, 2024
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About Author
Written by
Shumaila SaeedShumaila Saeed, an expert content creator with 6 years of experience, specializes in distilling complex topics into easily digestible comparisons, shining a light on the nuances that both inform and educate readers with clarity and accuracy.
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