Update empty values in column from the same column [duplicate] - mysql

Question

I have a simple mysql table:
CREATE TABLE IF NOT EXISTS `pers` (
`persID` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(35) NOT NULL,
`gehalt` int(11) NOT NULL,
`chefID` int(11) DEFAULT NULL,
PRIMARY KEY (`persID`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=4 ;
INSERT INTO `pers` (`persID`, `name`, `gehalt`, `chefID`) VALUES
(1, 'blb', 1000, 3),
(2, 'as', 1000, 3),
(3, 'chef', 1040, NULL);
I tried to run following update, but I get only the error 1093:
UPDATE pers P
SET P.gehalt = P.gehalt * 1.05
WHERE (P.chefID IS NOT NULL
OR gehalt <
(SELECT (
SELECT MAX(gehalt * 1.05)
FROM pers MA
WHERE MA.chefID = MA.chefID)
AS _pers
))
I searched for the error and found from mysql following page http://dev.mysql.com/doc/refman/5.1/en/subquery-restrictions.html, but it doesn't help me.
What shall I do to correct the sql query?

Answer 1

The problem is that MySQL, for whatever inane reason, doesn't allow you to write queries like this:
UPDATE myTable
SET myTable.A =
(
SELECT B
FROM myTable
INNER JOIN ...
)
That is, if you're doing an UPDATE/INSERT/DELETE on a table, you can't reference that table in an inner query (you can however reference a field from that outer table...)
The solution is to replace the instance of myTable in the sub-query with (SELECT * FROM myTable), like this
UPDATE myTable
SET myTable.A =
(
SELECT B
FROM (SELECT * FROM myTable) AS something
INNER JOIN ...
)
This apparently causes the necessary fields to be implicitly copied into a temporary table, so it's allowed.
I found this solution here. A note from that article:
You don’t want to just SELECT * FROM table in the subquery in real life; I just wanted to keep the examples simple. In reality, you should only be selecting the columns you need in that innermost query, and adding a good WHERE clause to limit the results, too.

Answer 2

You can make this in three steps:
CREATE TABLE test2 AS
SELECT PersId
FROM pers p
WHERE (
chefID IS NOT NULL
OR gehalt < (
SELECT MAX (
gehalt * 1.05
)
FROM pers MA
WHERE MA.chefID = p.chefID
)
)
...
UPDATE pers P
SET P.gehalt = P.gehalt * 1.05
WHERE PersId
IN (
SELECT PersId
FROM test2
)
DROP TABLE test2;
or
UPDATE Pers P, (
SELECT PersId
FROM pers p
WHERE (
chefID IS NOT NULL
OR gehalt < (
SELECT MAX (
gehalt * 1.05
)
FROM pers MA
WHERE MA.chefID = p.chefID
)
)
) t
SET P.gehalt = P.gehalt * 1.05
WHERE p.PersId = t.PersId

Answer 3

In Mysql, you can not update one table by subquery the same table.
You can separate the query in two parts, or do
UPDATE TABLE_A AS A
INNER JOIN TABLE_A AS B ON A.field1 = B.field1
SET field2 = ?

Answer 4

Make a temporary table (tempP) from a subquery
UPDATE pers P
SET P.gehalt = P.gehalt * 1.05
WHERE P.persID IN (
SELECT tempP.tempId
FROM (
SELECT persID as tempId
FROM pers P
WHERE
P.chefID IS NOT NULL OR gehalt <
(SELECT (
SELECT MAX(gehalt * 1.05)
FROM pers MA
WHERE MA.chefID = MA.chefID)
AS _pers
)
) AS tempP
)
I've introduced a separate name (alias) and give a new name to 'persID' column for temporary table

Answer 5

It's quite simple. For example, instead of writing:
INSERT INTO x (id, parent_id, code) VALUES (
NULL,
(SELECT id FROM x WHERE code='AAA'),
'BBB'
);
you should write
INSERT INTO x (id, parent_id, code)
VALUES (
NULL,
(SELECT t.id FROM (SELECT id, code FROM x) t WHERE t.code='AAA'),
'BBB'
);
or similar.

Answer 6

The Approach posted by BlueRaja is slow I modified it as
I was using to delete duplicates from the table. In case it helps anyone with large tables
Original Query
DELETE FROM table WHERE id NOT IN (SELECT MIN(id) FROM table GROUP BY field 2)
This is taking more time:
DELETE FROM table WHERE ID NOT IN(
SELECT MIN(t.Id) FROM (SELECT Id, field2 FROM table) AS t GROUP BY field2)
Faster Solution
DELETE FROM table WHERE ID NOT IN(
SELECT t.Id FROM (SELECT MIN(Id) AS Id FROM table GROUP BY field2) AS t)

Answer 7

MySQL doesn't allow selecting from a table and update in the same table at the same time. But there is always a workaround :)
This doesn't work >>>>
UPDATE table1 SET col1 = (SELECT MAX(col1) from table1) WHERE col1 IS NULL;
But this works >>>>
UPDATE table1 SET col1 = (SELECT MAX(col1) FROM (SELECT * FROM table1) AS table1_new) WHERE col1 IS NULL;

Answer 8

MariaDB has lifted this starting from 10.3.x (both for DELETE and UPDATE):
UPDATE - Statements With the Same Source and Target
From MariaDB 10.3.2, UPDATE statements may have the same source and target.
Until MariaDB 10.3.1, the following UPDATE statement would not work:
UPDATE t1 SET c1=c1+1 WHERE c2=(SELECT MAX(c2) FROM t1);
ERROR 1093 (HY000): Table 't1' is specified twice,
both as a target for 'UPDATE' and as a separate source for data
From MariaDB 10.3.2, the statement executes successfully:
UPDATE t1 SET c1=c1+1 WHERE c2=(SELECT MAX(c2) FROM t1);
DELETE - Same Source and Target Table
Until MariaDB 10.3.1, deleting from a table with the same source and target was not possible. From MariaDB 10.3.1, this is now possible. For example:
DELETE FROM t1 WHERE c1 IN (SELECT b.c1 FROM t1 b WHERE b.c2=0);
DBFiddle MariaDB 10.2 - Error
DBFiddle MariaDB 10.3 - Success

Answer 9

Just as reference, you can also use Mysql Variables to save temporary results, e.g.:
SET #v1 := (SELECT ... );
UPDATE ... SET ... WHERE x=#v1;
https://dev.mysql.com/doc/refman/5.7/en/user-variables.html

Answer 10

If you are trying to read fieldA from tableA and save it on fieldB on the same table, when fieldc = fieldd you might want consider this.
UPDATE tableA,
tableA AS tableA_1
SET
tableA.fieldB= tableA_1.filedA
WHERE
(((tableA.conditionFild) = 'condition')
AND ((tableA.fieldc) = tableA_1.fieldd));
Above code copies the value from fieldA to fieldB when condition-field met your condition. this also works in ADO (e.g access )
source: tried myself

Answer 11

Other workarounds include using SELECT DISTINCT or LIMIT in the subquery, although these are not as explicit in their effect on materialization. this worked for me
as mentioned in MySql Doc