Disadvantages of quoting integers in a Mysql query?

Question

I am curious about the disadvantage of quoting integers in MYSQL queries

For example

SELECT col1,col2,col3 FROM table WHERE col1=\'3\';

Answer 1

According to me, I think there is no performance/size cost in the case you have mentioned. Even if there is, then it is very much negligible and wont affect your application as such.

Answer 2

Strings also have a different sort order from numbers.

Compare:

SELECT 312 < 41

(yields 0, because 312 numerically comes after 41)

to:

SELECT '312' < '41'

(yields 1, because '312' lexicographically comes before '41')

Depending on the way your query is built using quotes might give wrong results or none at all.

Numbers should be used as such, so never use quotes unless you have a special reason to do so.

Answer 3

It gives the wrong impression about the data type for the column. As an outsider, I assume the column in question is CHAR/VARCHAR & choose operations accordingly.

Otherwise MySQL, like most other databases, will implicitly convert the value to whatever the column data type is. There's no performance issue with this that I'm aware of but there's a risk that supplying a value that requires explicit conversion (using CAST or CONVERT) will trigger an error.

Answer 4

The performance cost is that whenever mysql needs to do a type conversion from whatever you give it to datatype of the column. So with your query

SELECT col1,col2,col3 FROM table WHERE col1='3';

If col1 is not a string type, MySQL needs to convert '3' to that type. This type of query isn't really a big deal, as the performance overhead of that conversion is negligible.

However, when you try to do the same thing when, say, joining 2 table that have several million rows each. If the columns in the ON clause are not the same datatype, then MySQL will have to convert several million rows every single time you run your query, and that is where the performance overhead comes in.