Difference Between ALTER and UPDATE (With Table)

SQL’s two altering instructions are ALTER as well as UPDATE. ALTER is often 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.


The main difference between Alter and Update is that the ALTER command utilizes Data Definition Language (DDL). On the other hand, the UPDATE Command, from the other end, is just a Data Manipulation Language (DML). Also, the syntax used in both of them is different too.

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 often 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 Between ALTER and UPDATE

Parameters of Comparison




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.


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 often used to add, erase, or edit the values of database relations.

The UPDATE statement is often 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 often 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.


The ALTER command displays the layout of relations within databases. The UPDATE command is being used to alter the attributes of the relation’s entries or tuples. Alter is a declarative language. The update command is just a programming language for manipulating data. Change the table structure, table title, sp, and functions, for instance. Modify the dataset in a row or column for illustration. The Alter command modifies the data table. The update function makes adjustments within the table. The update command is often used to make modifications to current records in a database.


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