How to update field to add value to existing value?

Question

How to update field to add value to existing value?
For example I have

Table name: table

id   credit
1      4
2      5
3      3


        

Answer 1

well '+' is an operator so u need to provide the parameter it requires. '+' operator is an binary operator thus we need to provide two parameters to it with the syntax

 value1+value2

though it may take parameters of many data types by writing '+7' you are only sending a String value "+7" replacing your previous value

so u better use

UPDATE table SET credit = '+7' WHERE id='1'

don't confuse '+' operator with other increment operators

Answer 2

I wanted to add to this with an 'ON DUPLICATE KEY UPDATE' example(based on the answer by @hims056). I found this answer but needed 'ON DUP...' so I figured may as well post it here.

INSERT INTO table1 
(`id`, `credit`)
VALUES (1, 4)
ON DUPLICATE KEY UPDATE
`credit` = `credit` + 7;

See the SQL Fiddle here

Answer 3

UPDATE table SET credit = credit + 7 WHERE id = 1

Answer 4

Simply use credit = credit + 7 instead of credit = '+7' in UPDATE statement

UPDATE tablename SET credit = credit + 7 WHERE id = 1

See this SQLFiddle

Answer 5

Just try this...

UPDATE table SET credit = credit + 7 WHERE id = 1

Answer 6

This is just a simple UPDATE. Try the following.

UPDATE tableName
SET Credit = Credit + 7
WHERE ID = 1

note that ID = 1 and ID = '1' is the same as the server automatically parses it.