SQL Server: What does 1 ++ 2 mean?

Question

SQL Server\'s T-SQL syntax seems to allow multiple plus signs in succession:

SELECT 1 + 2 --3
SELECT 1 ++ 2 --3
SELECT 1 ++++++ 2 --3
SELECT 1 + \'2\' --3
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Answer 1

SELECT 1 ++ 2 means 1 plus (+2) which means 3

Same logic for the others 1+(+(+2)) and so on

SELECT '1' + '2' --'12' you are concatenating 2 strings, string '1' and string '2', which results '12'

Answer 2

The first plus sign is interpreted as an addition operator. Each of the remaining plus signs is interpreted as a unary plus operator:

1 ++ 2   means   1 + (+2)
1 +++ 2  means   1 + (+(+2))

It's very common in programming languages to have this unary plus operator, though it's rarely used in SQL as it doesn't actually do anything.

Although a unary plus can appear before any numeric expression, it performs no operation on the value returned from the expression. Specifically, it will not return the positive value of a negative expression.

The unary plus operator is mentioned in the SQL-92 standard.

As well as the usual arithmetic operators, plus, minus, times, divide, unary plus, and unary minus, there are the following functions that return numbers: ...

While unary plus isn't all that useful, it has a more useful companion: unary minus. It is also known as the negative operator.

SELECT -(expression), ...
--     ^ unary minus