MySql How to set a local variable in an update statement (Syntax?)

Question

How can I set a variable while doing an Update statement? I can\'t seem to figure out the syntax.

So I want something like this below but it\'s saying the syntax is

Answer 1

The key is the ":=" operators. MySQL User Variable

You can also assign a value to a user variable in statements other than SET. In this case, the assignment operator must be := and not = because the latter is treated as the comparison operator = in non-SET statements:

1 Use the one of the updating column

SET @tempVariable := 0;

UPDATE myTable 
SET col1 = 5, 
    col2 = @tempVariable := 100, 
    col3 = @tempVariable := col2 + 1;

@tempVariable is always 100 and col3 will be always 101. Seems mySQL will use the new assigned value instead of original value in the table. This is different from MS SQL. To make it more clear, try the following example, the value will be 1001 for col3 and @tempVariable.

UPDATE myTable 
SET col1 = 5, 
    col2 = @tempVariable := 100, 
    col2 = 1000
    col3 = @tempVariable := col2 + 1;

2 Use other column in the table than the updating column.

UPDATE myTable 
SET col1 = 5, 
    col2 = @tempVariable := 100, 
    col3 = @tempVariable := col4 + 1;

@tempVariable and col3 will have the same value. They will be the col4 original value + 1.