The UPDATE statement can be used to update data in a table.

The WHERE clause can be used in order to specify exactly which rows should be updated.

You can update all rows, some rows, or none, depending on the filtering conditions applied by the WHERE clause.

A Simple Update

Here's a simple update that changes artist number 16 to Mothers of Invention:

UPDATE Artists

SET ArtistName = 'Mothers of Invention'

WHERE ArtistId = 16;

And verify the update with a quick SELECT:

sqlite> SELECT * FROM Artists WHERE ArtistId = 16;ArtistId              ArtistName                                          Bio--------------------  --------------------------------------------------  ----------16                    Mothers of Invention

Update all Rows

You can update all rows of a table simply by omitting the WHERE clause.

Let's try it:

UPDATE Artists

SET Bio = 'Australian jazz band centred around polyrhythms.';

And check it with a SELECT statement:

sqlite> SELECT ArtistName, Bio FROM Artists;ArtistName            Bio--------------------  --------------------------------------------------Joe Satriani          Australian jazz band centred around polyrhythms.Steve Vai             Australian jazz band centred around polyrhythms.The Tea Party         Australian jazz band centred around polyrhythms.Noiseworks            Australian jazz band centred around polyrhythms.Wayne Jury            Australian jazz band centred around polyrhythms.Mr Percival           Australian jazz band centred around polyrhythms.Iron Maiden           Australian jazz band centred around polyrhythms.Atmasphere            Australian jazz band centred around polyrhythms.Ian Moss              Australian jazz band centred around polyrhythms.Magnum                Australian jazz band centred around polyrhythms.Strapping Young Lad   Australian jazz band centred around polyrhythms.Slayer                Australian jazz band centred around polyrhythms.Primus                Australian jazz band centred around polyrhythms.Pat Metheny           Australian jazz band centred around polyrhythms.Frank Gambale         Australian jazz band centred around polyrhythms.Mothers of Invention  Australian jazz band centred around polyrhythms.The Wiggles           Australian jazz band centred around polyrhythms.

Oops! I don't think all these bands are Australian jazz bands centred around polyrhythms.

Not to worry, we can fix that. We can set that column to NULL for all artists that this bio doesn't apply to. In this case, the bio only applies to artist ID 8 so we'll null all rows where the ArtistId is not equal to 8.

UPDATE Artists

SET Bio = NULL

WHERE ArtistId <> 8;

And now the bio is only stored against the correct artist.

sqlite> SELECT ArtistName, Bio FROM Artists;ArtistName            Bio--------------------  --------------------------------------------------Joe SatrianiSteve VaiThe Tea PartyNoiseworksWayne JuryMr PercivalIron MaidenAtmasphere            Australian jazz band centred around polyrhythms.Ian MossMagnumStrapping Young LadSlayerPrimusPat MethenyFrank GambaleMothers of InventionThe Wiggles

Careful!

It is extremely convenient for us that all bios previously contained NULL values. This meant that we could simply set them back to NULL and walk away.

This would've been a whole lot trickier if the other artists already had full bios. Setting them back to NULL does not bring back their old bios. So be careful when updating data.