Sunday, 16 February 2014

Update statement in SQL

Update statement in SQL

Update statement in SQL is generally to update a value in a table. We should generally be very conscious while using this statement. If you do not specify where clause in update statement all the records in the specified column will be updated with the mentioned value and the entire column will contain only one value

Consider below table 'test'

If we use a Update statement as below without any where condition then all the values fname will be set to 'ABCD' i.e. all the four rows in the fname column will have 'ABCD' as value

update table test
set fname = 'ABCD'

Hence, it is always recommended that you specify a where condition which fulfill all the criteria, as below

update table test
set fname = 'ABCD' where lname = 'abc1'

Here, only the row which has 'abc1' as lname will be updated

We can also update multiple columns in a single update statement as below

Update table tablename
Set Column1= '', Column2='',......

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