Can anyone explain :: meaning in postgresql?

Question

I have below query which works properly but don't know meaning and use of :: in postgresql.

select (
    select ( 
        case when 1 > 0 then 1::float / (
            select count(id) from transactions_products where transaction_id in (
            select id from transactions_transactions tt 
            where status = 3 and fi = 355 
                and (invoice_date >= 1420754400) 
                and (invoice_date <= 1421099999) 
                and (tt.division_id = 107) 
                and (tt.department_id = 210) 
        ) and is_vehicle = 1 
    )::float else 0 end)
 limit 1) as f_4

There's a few [related questions](http://stackoverflow.com/questions/5758499/double-colon-notation-in-sql) here, but they seem to relate to PostgreSQL. — halfer, Jan 12 '15 at 13:33
http://stackoverflow.com/questions/5758499/double-colon-notation-in-sql — Patrick Q, Jan 12 '15 at 13:36

score 11 · Accepted Answer · edited Jan 12 '15 at 13:38

11

:: is the cast operator for PostgreSQL.

edited Jan 12 '15 at 13:38

answered Jan 12 '15 at 13:36

Jay Blanchard

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Is it not possible in mysql? – Sandeep Jan 12 '15 at 13:39
Yes - using [`cast()`](http://dev.mysql.com/doc/refman/5.0/en/cast-functions.html) – Jay Blanchard Jan 12 '15 at 13:40
2

And CAST() is also standard SQL, works in many databases that support some form of SQL. – Frank Heikens Jan 12 '15 at 15:10

score 0 · Answer 2 · answered Jan 12 '15 at 13:31

0

Short, no-hassle answer: It casts the value to a float.

answered Jan 12 '15 at 13:31

rdiz

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You might want to elaborate on your answer. It's not really useful to just say it casts the value. Why would you want to cast a value? Is there a better example of a use case? – Machavity Jan 12 '15 at 13:38
I see what you mean, but then the post would just turn into a general discussion of the purpose, pros and cons of typecasting. – rdiz Jan 12 '15 at 13:41
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You don't need to go into that level of detail, just explain why you would use one or provide something for the OP to go on. You're assuming that everyone knows what casting is. Note the top answer has a link to more information. – Machavity Jan 12 '15 at 13:44
That is indeed a better answer. Thank you for your feedback! – rdiz Jan 12 '15 at 13:44

Can anyone explain :: meaning in postgresql?

2 Answers2