How to golf evaluation of math expression in MySQL? The challenge given to me is comparatively easy, and specific to MySQL only. I'm given a table expressions which have mathematical calculations done by a kid. Basically, I've to select all the right calculations!
The table have the following properties,

a : an integer, the left operand.
b : an integer, the right operand.
operation : a char, any one operation from '+', '-', '*' and '/' (pure-div).
c : an integer, the result given by the kid.

Example
a  b  operation  c
------------------
2  3  +          5
4  2  /          3
6  1  *          9
8  5  -          3

As we can see, the second and third operations are wrongly calculated, so they need to be filtered out. Here is what I've done till now,
MySQL, 88 chars
Rule: 88 chars is calculated by removing all spaces (\s+) from the given code. This is MySQL, so they simply take amount of chars (calculated here).

select * from expressions
where if(
    '+' = @o := operation,
    a + b,
    if(
        @o = '-',
        a - b,
        if(
            @o = '*',
            a * b,
            a / b
        )
    )
) = c

Try it on Rextester!
But, I'm sure that this can be golfed further, as many other submissions are of 73 chars, which is 15 bytes fewer than mine!
I think I need to change the idea of my solution, but I can't find anything which can evaluate expressions directly in MySQL. Any ideas?
Rules

The names, specific to table, included in the code isn't subject to change.
select is considered to be the only method to output/result.
For multiple statements, it should be wrapped inside begin ... end, as the whole code is the body of a function, defined as,
CREATE PROCEDURE expressionsVerification()
Score 69
select * from expressions
where elt(ord(operation)/2-20,a*b,a+b,a-b,a/b)=c

Takes inspiration from Marmite Bomber's use of elt, but uses a magic formula. Indexes into the list via ord(operation)2/-20, which buckets the four character codes across 1 to 4 by abusing elt's rounding behavior.
-1 thanks to Arnauld, who improved on the modulo reduction.
-1 thanks to Bubbler, who found a better non-modulo formula.
Score 73
select * from expressions
where elt(instr('*/-+',operation),a*b,a/b,a-b,a+b)=c

This is my best guess as to the 73 you mention other people have gotten in the question.