51 SQL DML Update

Update statements is used to update rows in the tables. Update should always be used with where clause. If where clause is forgotten, then every row in the table is updated.

Following sql will work on command line normally.

UPDATE Employee
SET City='DENEME'

But dbeaver gives a warning for dangerous sql. But be aware that not every tool gives this warning. Especially, programmatic connections run every sql normally.

dbeaver-dangerous-sql-update-without-where

See following database specific documentation

sqlite update

51.1 Single row

For single row update, we should use where PK_Column = value filter in our update statements. Following update statement will only update the row with employee id 5 value.

UPDATE Employee
SET City='DENEME'
WHERE EmployeeId=5;

51.2 Multiple rows

Before updating multiple values with update statements, we should first run the select count(*) statement to see how many rows we are updating and this row count is consistent with our expectations.

Following sql return 3,

SELECT COUNT(*) FROM Customer 
WHERE FirstName LIKE 'A%'

then corresponding update statement will update 3 rows.

UPDATE Customer
SET City='DENEME'
WHERE FirstName LIKE 'A%';