Update from SQL Server

Hello Dev! In this journal article, we are going to discuss everything about updating from SQL Server. SQL Server is a popular database management system that plays a crucial role in the functioning of many applications. Updating data in SQL Server can be a complex task, but with the proper knowledge and resources, it can be accomplished efficiently. This article will guide you in updating data from SQL Server.

Understanding SQL Server Updates

In SQL Server, updating data means changing the current value of a particular column in a table. We can update data in SQL Server using the SQL Update statement. The Update statement has different clauses, such as the set clause, where clause, and join clause, which help us modify the desired data.

The following is an example of an update statement in SQL Server:

Column A	Column B	Column C
Value 1	Value 2	Value 3
Value 4	Value 5	Value 6
Value 7	Value 8	Value 9

Let us say we want to update the value of Column B to ‘Value 10’ where Column A is equal to ‘Value 1’. The SQL Update statement for this can be written as:

UPDATE Table SET ColumnB = 'Value 10' WHERE ColumnA = 'Value 1';

This will change the value of Column B in the first row of the table to ‘Value 10’.

Updating from a Single Table

Updating data from a single table is the simplest way to modify data in SQL Server. The update statement is used to update data from a single table. We can use the Where clause to specify the conditions for which rows to update.

The following is an example of updating data from a single table:

Column D	Column E	Column F
Value 1	Value 2	Value 3
Value 4	Value 5	Value 6
Value 7	Value 8	Value 9

To update the Value of Column F to ‘Value 11’ where Column D is equal to ‘Value 1’, the SQL Update statement for this can be written as:

UPDATE Table SET ColumnF = 'Value 11' WHERE ColumnD = 'Value 1';

This will change the value of Column F in the first row of the table to ‘Value 11’.

Updating from Multiple Tables

Updating data from multiple tables is more complex than updating data from a single table. It can be done using the SQL Join statement. We can use the Join clause to combine two or more tables and update specific values in these tables.

The following is an example of updating data from multiple tables:

Column G	Column H
Value 1	Value 2
Value 3	Value 4

Column I	Column J
Value 1	Value 2
Value 3	Value 4

In this example, we are going to update the value of Column H in the first table to ‘Value 5’ where Column G is equal to ‘Value 1’. The SQL statement for this can be written as:

UPDATE Table1 SET ColumnH = 'Value 5' WHERE ColumnG = 'Value 1' JOIN Table2 ON Table1.ColumnG = Table2.ColumnI;

This statement will update the value of Column H in the first table, and also join the table on a particular column for modification of data.

FAQ

What happens if I update a column that has a primary key?

If a column that has a primary key is updated, it will change the value of the primary key for that row. This can cause data discrepancies and should be avoided.

Can I update multiple rows at once?

Yes, you can update multiple rows at once by using the IN clause.

Can I undo an update statement?

No, once an update statement is executed, the changes made cannot be undone. You can, however, use a backup to restore the previous data.

What is the difference between an update and an insert statement?

An update statement is used to modify existing data in a table, while an insert statement is used to add new data to a table.

What is the syntax for the Update statement?

The syntax for the Update statement is as follows:

UPDATE [Table Name] SET [Column Name] = [New Value] WHERE [Condition];

Conclusion

Updating data from SQL Server can be a challenging task, but with the proper understanding of the update statement and its clauses, this can be done efficiently. We have discussed how to update data from a single table and multiple tables, some frequently asked questions, and the syntax for the Update statement. We hope this article has been helpful in providing insights into updating data from SQL Server.