MySQL move part of a cell to another column - mysql

Question

I have the following imported to TableA, Column 'Clothes' and Column 'Colours'
The problem is the import has put in the 'Clothes' column 'Jeans - Blue' and 'Jumper - Red' etc etc
Please could someone help me with a query to keep everything before the - in 'Clothes' and everything after the - into 'Colours' and removing the - altogether.

Answer 1

Two steps for this.
First, update the colors:
UPDATE yourTableA T
SET T.Colours = TRIM(SUBSTR(T.Clothes,INSTR(T.Clothes,'-') + 2));
Second, update the Clothes:
UPDATE yourTableA T
SET T.Clothes = TRIM(SUBSTR(T.Clothes,1,INSTR(T.clothes,'-')-1));
I've used SUBSTR as my string swiss army knife here, and INSTR to locate the position of the - in between. You can do without TRIM, but I usually use this in those cases to avoid unnecessary white spaces.
There surely are more direct ways to do it, but this'll work.

Answer 2

The SUBSTRING_INDEX function is convenient, and the TRIM function can remove leading and trailing spaces. For example:
SELECT TRIM(SUBSTRING_INDEX(a.Clothes,'-',1)) AS Clothes
, TRIM(SUBSTRING_INDEX(a.Clothes,'-',-1)) AS Colours
FROM TableA a
WHERE LENGTH(a.Clothes)-LENGTH(REPLACE(a.Clothes,'-','')) = 1
(NOTE: the query above is returning the substring before the first '-' character, and is returning the substring after the last '-' character. So any values with more than one dash would lose the portion between the first and last dashes, consider e.g. 'A - B - C - D', the query above returns the A and returns the D, and loses everything else.
To handle this anomaly, the WHERE clause checks that the string contains a single occurrence of the '-' character.
Once you have a query you are happy with, you can turn that into an UPDATE statement, BUT be VERY careful about the order you assign new values to columns. Unlike other relational databases, MySQL does not guarantee that a reference to an existing column within the statement will be the value of the column from the beginning of the statement... the only guarantee is that it will be the value that is currently assigned. So, the order that the columns is assigned is important!
UPDATE TableA a
SET Colours = TRIM(SUBSTRING_INDEX(a.Clothes,'-',-1))
, Clothes = TRIM(SUBSTRING_INDEX(a.Clothes,'-',1))
WHERE LENGTH(a.Clothes)-LENGTH(REPLACE(a.Clothes,'-','')) = 1
Note that if we were to assign the Clothes column before we assigned a value to the Colours column, the value we want assigned to Colours would be "lost".

Answer 3

You can do it in a single UPDATE as follows:
UPDATE TableA
SET `Colours` = SUBSTRING_INDEX(`Clothes`, ' - ', -1),
`Clothes` = SUBSTRING_INDEX(`Clothes`, ' - ', 1)
;
You can experiment with SQL Fiddle Demo I created from your data.
Here's the data I worked with:
CREATE TABLE TableA
(Clothes varchar(20), Colours varchar(20))
;
INSERT INTO TableA
(`Clothes`, `Colours`)
VALUES
('Jeans - Blue', NULL),
('Jumper - Red', NULL)
;
This the result of SELECT * FROM TableA; :
CLOTHES COLOURS
Jeans Blue
Jumper Red