UPDATE changes the values of the specified columns in all rows that satisfy the condition. Only the columns to be modified need be mentioned in the SET clause; columns not explicitly modified retain their previous values.

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5
votes
6answers
363 views

Backup very large table

I have to update certain values of a large table (for the sake of a presumed example, it is called 'Resource' and it is over 5M rows) and thus I have to make a backup before performing the changes. We ...
2
votes
3answers
507 views

Problem with nested UPDATE queries

I cannot make an update query work. As a first step, the following one works correctly: UPDATE Tab1 SET Tab1.a = '3' WHERE Tab1.id IN ( 123, 456 ); where id is the primary key of Tab1. ...
2
votes
3answers
773 views

INNER JOIN Giving time out on large database

Getting time out on this script UPDATE uk_data AS ud INNER JOIN uk_pc AS up ON ud.cat10 = up.WardCode SET ud.cat8 = up.Latitude, ud.cat9 = up.Longitude; uk_pc Table ...
5
votes
2answers
3k views

Optimizing bulk update performance in Postgresql

Using PG 9.1 on Ubuntu 12.04. It currently takes up to 24h for us to run a large set of UPDATE statements on a database, which are of the form: UPDATE table SET field1 = constant1, field2 = ...
4
votes
2answers
6k views

Update many rows in a table with a single statement?

What is the easiest way to update many rows in a table? I have a csv file that looks like this: |primary_key |value| | 1 | xyz| | 2 | abc| | 3 | def| ... Rows with ...
3
votes
1answer
538 views

Update rank on a large table

I have a mysql table that has now 12 million records and I'm trying to update a column (rank) with the following UPDATE code: SET @r=0; UPDATE records SET rank= @r:= (@r+1) where type = 2 ORDER BY ...
2
votes
1answer
340 views

Update ranking on table

I have two tables: mysql> desc rank ; +----------------+-------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | ...
2
votes
2answers
2k views

GROUP BY two columns

I want to count two columns, but need to get the results of first column in one row. SELECT country, COUNT(*) FROM table1 GROUP BY country, type This query gives me country type COUNT(*) ...
1
vote
2answers
71 views

Is column order reliable in UPDATE?

Can we reply on the order of columns in an UPDATE? SET @x = 0 UPDATE table1 SET col1=IF(col1 IS NULL, NULL, @x:=@x+col1), col2=IF(col2 IS NULL, NULL, @x:=@x+col2), col3=IF(col3 IS NULL, NULL, @x:=0) ...