Mysql – Multiple update of records in the same table

MySQLupdate

I have an update query e.g.:

UPDATE table SET name = ? WHERE id = ?

I have all the relevant ids collected. I am looping over the ids and executing the update query for each one. In pseudo code:

for (id..ids)  {
   stmt->executeUpdate(query, nameForId(id), id);  
}

I was wondering is there a smarter/more efficient way to do this query update without looping? For instance, is there a way to create a big string once, like:

UPDATE table set a=? where id=? AND a=? where id=? ...etc.

Best Answer

Philᵀᴹ: Insert all of the data pairs into a temporary staging table, then run a single update. Will be lots quicker.

Kondybas: Create table pairs(id,name) from collected data and then:

UPDATE table 
JOIN pairs ON table.id=pairs.id
SET table.name=pairs.name

_{Wiki answer generated from comments on the question.}

OPTION #1 : INSERT INTO ... ON DUPLICATE KEY UPDATE

INSERT INTO newtable
SELECT * FROM oldtable
ORDER BY tmstamp_value
ON DUPLICATE KEY UPDATE email=VALUES(email), address=VALUES(address) ... ;

OPTION #2 : REPLACE INTO

REPLACE INTO newtable
SELECT * FROM oldtable
ORDER BY tmstamp_value;

It mechanically performs a DELETE and an INSERT.

CAVEAT

Notice I applied the ORDER BY against the old table. This should help get the latest data for a give LastName, FirstName.

You should also add a UNIQUE INDEX on the new table as follows:

ALTER TABLE newtable ADD UNIQUE INDEX name_ndx (lastname,firstname);

UPDATE 2013-04-08 17:13 EDT

If you are doing updates, there are two ways to do this:

1. UPDATE JOIN

UPDATE
(SELECT lastname,firstname,phone,email
FROM oldtable ORDER BY lastname,firstname) A
LEFT JOIN newtable B USING (lastname,firstname)
SET B.phone=A.phone,B.email=A.email;

2. UPDATE JOIN with GROUP BY

UPDATE
(
    SELECT BB.id,BB.phone,BB.email FROM 
    (SELECT lastname,firstname,MAX(id) id FROM oldtable GROUP BY lastname,firstname) AA
    INNER JOIN oldtable BB USING (lastname,firstname)
) A INNER JOIN newtable B USING (id)
SET B.phone=A.phone,B.email=A.email;

Give it a Try !!!

Both options will take full advantage of the UNIQUE index on name.

Sql-server – How to update ID=null values in table to incremental counter values

You can do this.

WITH T
     AS (SELECT ISNULL((SELECT MAX(ID) FROM StagingTable), 0) + 
                    ROW_NUMBER() OVER (ORDER BY NaturalID) AS New_ID,
                ID
         FROM   StagingTable
         WHERE  ID IS NULL)
UPDATE T
SET    ID = New_ID

So the windowed function is used in the SELECT list but you can still use the result of it to UPDATE the column.

You should probably have a filtered index unique constraint on ID WHERE ID IS NOT NULL to prevent duplicates too. Or run this at serializable isolation level to block concurrent inserts.