Why is ' 2' > '10'?

Question

Why is \' 2\' with an initial space bigger than \'10\'?

select \' 2\' > \'10\';
 ?column? 
----------
 t
(1 row)

I tried i

Answer 1

I think PostgreSQL automatically tries to figure out the type behind the scenes and in Linux it tries to get rid of the ' ', some of the comparisons are also based on locale.

• Thus, ' 2' > '10' becomes '2'>'10' and the comparison is '2'>'1'; they are not equal, so no need to continue with the rest of the string, and ascii('2') is greater than ascii('1'), so it evaluates to true.

• If it were an equality operation (e.g. ' 22' = '22 ') it would result to false because Postgres does a byte by byte comparison. This is important because the engine uses two different algorithms when doing comparisons.

• If you specify the type via typecasting, then it won't override the space rules (' '=>'').

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Also credit goes to: RhodiumToad and Peerce in #postgresql

Answer 2

I think this has to do with locale settings.

According to PostgreSQL docs: Locale Support:

The locale settings influence the following SQL features:

• Sort order in queries using ORDER BY on textual data
• The ability to use indexes with LIKE clauses
• The upper, lower, and initcap functions
• The to_char family of functions