ALTER vs UPDATE: Difference and Comparison

SQL’s two altering instructions are ALTER as well as UPDATE. ALTER is used to change the dynamics of the database’s relations. Whereas, the UPDATE statement is then used to amend data held in a database relation.

The primary distinction between ALTER and UPDATE commands would be that ALTER offers a DDL command, whereas UPDATE is based on a Data Manipulation Language command.

Key Takeaways

1. Alter refers to making changes or modifications to something, to improve or customize it. In contrast, an update refers to updating something by incorporating the latest changes or information.
2. Alterations can be significant or minor and can be made to various things such as clothing, furniture, or documents. In contrast, updates are made to software, technology, or information systems.
3. Alterations may involve changing the original design or structure of something, while updates maintain the original design or structure but add new features or fix issues.

ALTER vs UPDATE

Alter refers to the process of making structural changes to a database schema. Update, on the other hand, refers to the process of modifying existing data within a database. Updating a database might involve changing the value of a single field within a record or updating multiple records at once.

A DDL (Data Definition Language) declaration is the ALTER SQL function. ALTER gets used to modify the layout of a database table. It is also used to add, remove, or alter entries in a database that already exists.

Users can also utilize the SQL ALTER TABLE function to add and remove constraints from a table that already exists.

In SQL, an UPDATE statement is used to edit or modify existing database tables. It can also be considered a data transformation command that is being used to modify a table’s entries.

It could be used to modify a single row depending on criteria, all rows, or even a set of rows depending on the user-specified condition.

Comparison Table

Parameters of Comparison	ALTER	UPDATE
Connotation	ALTER is a SQL statement that is being used to edit an RDBMS’s datasets, tables, and so on.	UPDATE is just a SQL command which is used to change the rows inside an RDBMS’s table. As a result, this would be the primary distinction amongst ALTER as well as UPDATE in SQL.
Type of Command	When it comes to Alter, it is considered as Data Definition Language (DDL) command.	UPDATE is considered as Data Manipulation Language (DML) command.
Usability	The ALTER command modifies the schema of the database including associated objects.	UPDATE command modifies the contents in a data structure. As a result, this is yet the additional distinction between ALTER as well as UPDATE in SQL.
Mainly Used for	The ALTER function is used to add, erase, or edit the values of database relations.	The UPDATE statement is used to upgrade existing information in the database.
Sets Values as	By convention, the ALTER function sets all tuple entries to NULL.	UPDATE command assigns the values indicated in the query to the tuples.

What is ALTER?

The ALTER command is just a DDL function (Data Definition Language). This command alters the composition or description of existing relationships within the database. 

One may affect the dynamics of relation by adding columns, deleting or dropping columns, renaming a column’s title, resizing columns, or changing the file format of columns in an existing table (relation) inside the databases.

Since columns in a relation correspond to the characteristics of that relationship, one may claim that the ALTER command exclusively works on columns or attributes.

Once the ALTER command puts an extra column or attributes to a relationship, it by convention sets the state of that attribute to NULL, including all tuples.

ALTER TABLE is being used to create, remove, or change columns in an existing database. It is used to add or remove constraints from an existing database.

ADD has been used to insert new columns into an existing table. When we need to obtain more details, we don’t have to recreate the entire database; instead, ADD rushes to our aid.

What is UPDATE?

The UPDATE function is part of the Data Manipulation Language (DML). This alters the attributes of one or even more tuples inside a relation.

Whenever the WHERE clause has been used in conjunction well with the UPDATE command, it aids in the selection of tuples wherein attributes are to be changed.

If used in conjunction using UPDATE, this S ET clause defines the attribute names to be adjusted as well as the quantities that would be allocated to them. It can establish the attribute’s values to NULL or DEFAULT.

Statistics keep track of the data distribution of said column value(s) in the databases and also the overall rows.

It maintains the spread of attributes for indexes. Within every statistical collection, a histogram is constructed for the first database column to record this cardinality. For multi-column statistical items, data on the relationship of the elements inside gets also saved.

Main Differences Between ALTER and UPDATE

1. The difference between the ALTER and UPDATE commands would be that the ALTER command is just a Data Definition Language command (DDL). The UPDATE Function, from the other end, is a Data Manipulation Language (DML).
2. The ALTER command adds, deletes, alters, and renames relation parameters; meanwhile, the UPDATE command adjusts the contents of the entries in the relations.
3. By nature, the ALTER command sets the entries of all tuples or records to NULL. The UPDATE Instruction, from the other end, assigns the value indicated within the query to the relation’s tuples.
4. The ALTER command is mainly for attributes or columns. Meanwhile, the UPDATE command is for feature values.
5. The ALTER command updates the database layout as well as any conformity. The UPDATE command, on the other hand, alters the values of a data structure. As a corollary, this is another contrast between ALTER and UPDATE in SQL.

References

1. https://dl.acm.org/doi/abs/10.1145/273133.274318
2. https://dl.acm.org/doi/abs/10.1145/319732.319745

Last Updated : 13 July, 2023