将select的聚合结果分配给mySQL中的用户变量

Question

I am trying to save a user variable with a result of count function from a table.

Executing this query:

SELECT @var:=count(distinct(column1)) FROM table_name;

Returns:

@var:=count(distinct(column1))
41243

Then executing:

SELECT @var;

Returns:

@var
Blob

When I expected 41243.

When I assign a value to a user variable it works as expected.

What am I doing wrong?

Thanks.

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Edit: I corrected $var to @var.

I am issuing the query from mySQL Workbench for testing. I will use it eventually from PHP.

Another related question: Can I assign a SELECT result to a user variable without having the result (In my example: 41243) sent back to the client (as it will slow the query if I'm using it from PHP).

Answer 1

You simply have to convert the blob type return value:

SELECT @var:=count(distinct(column1)) FROM table1;
SELECT convert(@var,unsigned);

Because the result is blob (binary string), you simply have to convert it to integer (in this case unsigned int, but if you use 'signed', then you will get signed integer.

Hope this helps.